A period is all about defining when something begins and ends. Class periods usually last about forty-five minutes. Following the last food fight, there was a period of relative peace in the school.

You know that dot at the end of a sentence? That's a period too. It means the sentence is over. In sports, games are often divided into playing periods: an ice hockey game, for example, has three periods. If you're a dinosaur buff, you know that this word can also refer to expanses of geologic time. The stegosaurus lived during the Jurassic period, for example, while the Tyrannosaurus rex and triceratops lived during the Cretaceous period.

Definitions of period
  1. noun
    an amount of time
    “a time period of 30 years”
    “hastened the period of time of his recovery”
    “Picasso's blue period
    synonyms: period of time, time period
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    Bronze Age
    (archeology) a period between the Stone and Iron Ages, characterized by the manufacture and use of bronze tools and weapons
    Iron Age
    (archeology) the period following the Bronze Age; characterized by rapid spread of iron tools and weapons
    Stone Age
    (archeology) the earliest known period of human culture, characterized by the use of stone implements
    Eolithic Age
    the earliest part of the Stone Age marked by the earliest signs of human culture
    Paleolithic Age
    second part of the Stone Age beginning about 750,00 to 500,000 years BC and lasting until the end of the last ice age about 8,500 years BC
    Lower Paleolithic
    the oldest part of the Paleolithic Age with the emergence of the hand ax; ended about 120,000 years ago
    Middle Paleolithic
    the time period of Neanderthal man; ended about 35,000 years BC
    Upper Paleolithic
    the time period during which only modern Homo sapiens was known to have existed; ended about 10,000 years BC
    middle part of the Stone Age beginning about 15,000 years ago
    Neolithic Age
    latest part of the Stone Age beginning about 10,000 BC in the Middle East (but later elsewhere)
    Great Schism
    the period from 1378 to 1417 during which there were two papacies in the Roman Catholic Church, one in Rome and one in Avignon
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    test period, trial period
    a period of time during which someone or something is tested
    time frame
    a time period during which something occurs or is expected to occur
    an indefinite period of time
    a period of time when something (as a machine or factory) is not operating (especially as a result of malfunctions)
    a period of time when something (as a machine or factory) is functioning and available for use
    work time
    a time period when you are required to work
    time off
    a time period when you are not required to work
    a period of illness
    hospitalisation, hospitalization
    a period of time when you are confined to a hospital
    travel time
    a period of time spent traveling
    a more or less definite period of time now or previously present
    an indefinite period (usually marked by specific attributes or activities)
    elapsed time
    the time that elapses while some event is occurring
    continuance, duration
    the period of time during which something continues
    calendar week, week
    a period of seven consecutive days starting on Sunday
    the middle of a week
    field day
    a time of unusual pleasure and success
    life, life-time, lifespan, lifetime
    the period during which something is functional (as between birth and death)
    the period between birth and the present time
    the period from the present until death
    millenary, millennium
    a span of 1000 years
    bimillenary, bimillennium
    a span of 2000 years
    the period of time during which a place or position or nation is occupied
    a earlier period in someone's life (especially one that they have reason to keep secret)
    shelf life
    the length of time a packaged food or drug will last without deteriorating
    time period following childbirth when the mother's uterus shrinks and the other functional and anatomic changes of pregnancy are resolved
    the period following birth during which milk is secreted
    time of life
    a period of time during which a person is normally in a particular life state
    calendar day, civil day
    a day reckoned from midnight to midnight
    a day or period of time set aside for feasting and celebration
    day, daylight, daytime
    the time after sunrise and before sunset while it is light outside
    forenoon, morn, morning, morning time
    the time period between dawn and noon
    dark, night, nighttime
    the time after sunset and before sunrise while it is dark outside
    the time between sunset and midnight
    the period spent sleeping
    a period of ignorance or backwardness or gloom
    the period immediately before something
    the early part of night (from dinner until bedtime) spent in a special way
    hebdomad, week
    any period of seven consecutive days
    fortnight, two weeks
    a period of fourteen consecutive days
    a time period usually extending from Friday night through Sunday; more loosely defined as any period of successive days including one and only one Sunday
    Indian summer, Saint Martin's summer
    a period of unusually warm weather in the autumn
    the period of time that it takes for a planet (as, e.g., Earth or Mars) to make a complete revolution around the sun
    school, school day, schooltime
    the period of instruction in a school; the time period when school is in session
    twelvemonth, year, yr
    a period of time containing 365 (or 366) days
    a period of time occupying a regular part of a calendar year that is used for some particular activity
    half a year; a period of 6 months
    a period of 2 months
    one of the four-year intervals between Olympic Games; used to reckon time in ancient Greece for twelve centuries beginning in 776 BC
    a period of five years
    decade, decennary, decennium
    a period of 10 years
    a period of 100 years
    a period of four years
    a period of five years
    a period of 50 years
    a period of 25 years
    a fourth part of a year; three months
    phase of the moon
    a time when the Moon presents a particular recurring appearance
    the period of time taken by a particular planet (e.g. Mars) to make a complete rotation on its axis
    calendar month, month
    one of the twelve divisions of the calendar year
    the middle part of January
    the middle part of February
    the middle part of March
    the middle part of April
    the middle part of May
    the middle part of June
    the middle part of July
    the middle part of August
    the middle part of September
    the middle part of October
    the middle part of November
    the middle part of December
    time limit
    a time period within which something must be done or completed
    a limited period of time
    a period of three months; especially one of the three three-month periods into which human pregnancy is divided
    a special and memorable period
    silly season
    a time usually late summer characterized by exaggerated news stories about frivolous matters for want of real news
    Golden Age
    (classical mythology) the first and best age of the world, a time of ideal happiness, prosperity, and innocence; by extension, any flourishing and outstanding period
    silver age
    (classical mythology) the second age of the world, characterized by opulence and irreligion; by extension, a period secondary in achievement to a golden age
    bronze age
    (classical mythology) the third age of the world, marked by war and violence
    iron age
    (classical mythology) the last and worst age of the world
    Platonic year, great year
    time required for one complete cycle of the precession of the equinoxes, about 25,800 years
    regulation time
    (sports) the normal prescribed duration of a game
    extra time, overtime
    playing time beyond regulation, to break a tie
    season, time of year
    one of the natural periods into which the year is divided by the equinoxes and solstices or atmospheric conditions
    canicular days, canicule, dog days
    the hot period between early July and early September; a period of inactivity
    the middle of winter
    a recurrent time marked by major holidays
    a period of the year marked by special events or activities in some field
    age, long time, years
    a prolonged period of time
    long haul, long run
    a period of time sufficient for factors to work themselves out
    drought, drouth
    a prolonged shortage
    epoch, era
    a period marked by distinctive character or reckoned from a fixed point or event
    the normal time between successive generations
    prehistoric culture, prehistory
    the time during the development of human culture before the appearance of the written word
    a period during which something or somebody is dominant or powerful
    the continuous period of time during which something (a machine or a factory) operates or continues in operation
    early days, youth
    an early period of development
    an opening time period
    a later concluding time period
    a period of time considered as a resource under your control and sufficient to accomplish something
    nap, sleep
    a period of time spent sleeping
    lease, term of a contract
    the period of time during which a contract conveying property to a person is in effect
    half life, half-life
    the time required for something to fall to half its initial value (in particular, the time for half the atoms in a radioactive substance to disintegrate)
    lunar time period, tide
    there are usually two high and two low tides each day
    phase, stage
    any distinct time period in a sequence of events
    occurring in more than one stage
    the period during which someone (especially a guard) is on duty
    a period of time during which there is no war
    a period of time during which there is armed conflict
    duty tour, enlistment, hitch, term of enlistment, tour, tour of duty
    a period of time spent in military service
    the early (usually calm and harmonious) period of a relationship; business or political
    a 15-year cycle used as a chronological unit in ancient Rome and adopted in some medieval kingdoms
    prohibition, prohibition era
    the period from 1920 to 1933 when the sale of alcoholic beverages was prohibited in the United States by a constitutional amendment
    incubation period
    the period between infection and the appearance of symptoms of the disease
    rainy day
    a (future) time of financial need
    noviciate, novitiate
    the period during which you are a novice (especially in a religious order)
    bloom, blossom, efflorescence, flower, flush, heyday, peak, prime
    the period of greatest prosperity or productivity
    running time
    the length of time that a movie or tv show runs
    clotting time
    the time it takes for a sample of blood to clot; used to diagnose some clotting disorders
    air alert
    the time period during which military and civilian agencies are prepared for an enemy air attack
    question time
    a period during a parliamentary session when members of British Parliament may ask questions of the ministers
    real time
    (computer science) the time it takes for a process under computer control to occur
    real time
    the actual time that it takes a process to occur
    study hall
    a period of time during the school day that is set aside for study
    the period of time permitted by commercial usage for the payment of a bill of exchange (especially a foreign bill of exchange)
    the time period that is considered best for starting or finishing something
    a period of prolonged uncertainty
    the period or time when something was produced
    harvest, harvest time
    the season for gathering crops
    haying, haying time
    the season for cutting and drying and storing grass as fodder
    the final stage of the prophase of meiosis
    the fourth stage of the prophase of meiosis
    the first stage of the prophase of meiosis
    the third stage of the prophase of meiosis
    phase of cell division
    a stage in meiosis or mitosis
    the second stage of the prophase of meiosis
    uptime is 24 hours a day 7 days a week
    a period of time assigned for work
    face time
    work time spent at the location of or in the presence of other people
    compensatory time
    time off that is granted to a worker as compensation for working overtime
    contemporary world, modern times, modern world, present times
    the circumstances and ideas of the present age
    Roman times
    the time period during which Rome dominated Europe
    some point or period in time
    a time when coldness (or some other quality associated with death) is intense
    hard times
    a time of difficulty
    time passed in a particular bodily form
    OWLT, one-way light time
    the elapsed time it takes for light (or radio signals) to travel between the Earth and a celestial object
    RTLT, round-trip light time
    the elapsed time it takes for a signal to travel from Earth to a spacecraft (or other body) and back to the starting point
    the time taken to traverse a measured course
    a period of dullness or boredom (especially in a work of literature or performing art)
    residence time
    the period of time spent in a particular place
    the complete duration of something
    stint, stretch
    an unbroken period of time during which you do something
    time scale
    an arrangement of events used as a measure of duration
    note value, time value, value
    (music) the relative duration of a musical note
    week, workweek
    hours or days of work in a calendar week
    the recurring hours when you are not sleeping (especially those when you are working)
    work done in addition to regular working hours
    turnaround, turnaround time
    time need to prepare a vessel or ship for a return trip
    free time, spare time
    time available for hobbies and other activities that you enjoy
    day off
    a day when you are not required to work
    leisure, leisure time
    time available for ease and relaxation
    leave, leave of absence
    the period of time during which you are absent from work or duty
    days, years
    the time during which someone's life continues
    afterlife, hereafter
    life after death
    the period of finest development, happiness, or beauty
    age, eld
    a time of life (usually defined in years) at which some particular qualification or power arises
    neonatal period
    the first 28 days of life
    babyhood, early childhood, infancy
    the early stage of growth or development
    anal phase, anal stage
    (psychoanalysis) the second sexual and social stage of a child's development during which bowel control is learned
    genital phase, genital stage
    (psychoanalysis) the fifth sexual and social stage in a person's development occurring during adolescence; interest focuses on sexual activity
    latency period, latency phase, latency stage
    (psychoanalysis) the fourth period (from about age 5 or 6 until puberty) during which sexual interests are supposed to be sublimated into other activities
    oral phase, oral stage
    (psychoanalysis) the first sexual and social stage of an infant's development; the mouth is the focus of the libido and satisfaction comes from suckling and chewing and biting
    phallic phase, phallic stage
    (psychoanalysis) the third stage in a child's development when awareness of and manipulation of the genitals is supposed to be a primary source of pleasure
    the time of person's life when they are a child
    schooldays, schooltime
    the time of life when you are going to school
    the time of life between childhood and maturity
    the time period between the beginning of puberty and adulthood
    a period of two years immediately prior to the onset of puberty when growth and changes leading to sexual maturity occur
    puberty, pubescence
    the time of life when sex glands become functional
    the time of life between the ages of 12 and 20
    mid-twenties, twenties
    the time of life between 20 and 30
    the decade from 1900 to 1909
    the decade from 1530 to 1539
    1920s, twenties
    the decade from 1920 to 1929
    the decade from 1820 to 1829
    mid-thirties, thirties, thirty-something
    the time of life between 30 and 40
    1930s, thirties
    the decade from 1930 to 1939
    the decade from 1830 to 1839
    forties, mid-forties
    the time of life between 40 and 50
    1940s, forties
    the decade from 1940 to 1949
    the decade from 1840 to 1849
    fifties, mid-fifties
    the time of life between 50 and 60
    1950s, fifties
    the decade from 1950 to 1959
    the decade from 1850 to 1859
    the decade from 1750 to 1759
    mid-sixties, sixties
    the time of life between 60 and 70
    1960s, sixties
    the decade from 1960 to 1969
    the decade from 1860 to 1869
    the decade from 1760 to 1769
    golden years
    the time of life after retirement from active work
    mid-seventies, seventies
    the time of life between 70 and 80
    1970s, seventies
    the decade from 1970 to 1979
    the decade from 1870 to 1879
    the decade from 1770 to 1779
    eighties, mid-eighties
    the time of life between 80 and 90
    1980s, eighties
    the decade from 1980 to 1989
    1880s, eighties
    the decade from 1880 to 1889
    the decade from 1780 to 1789
    mid-nineties, nineties
    the time of life between 90 and 100
    1990s, nineties
    the decade from 1990 to 1999
    1890s, nineties
    the decade from 1890 to 1899
    the decade from 1790 to 1799
    bloom, bloom of youth, salad days
    the best time of youth
    adulthood, maturity
    the period of time in your life after your physical growth has stopped and you are fully developed
    the time of a man's life prior to marriage
    middle age
    the time of life between youth and old age (e.g., between 40 and 60 years of age)
    the time of a woman's life when she is a widow
    age, eld, geezerhood, old age, years
    a late time of life
    the last few hours before death
    a day assigned to a particular purpose or observance
    the particular day, month, or year (usually according to the Gregorian calendar) that an event occurred
    church festival, religious festival
    a festival having religious significance
    day of the week
    any one of the seven days in a week
    the part of the day between noon and evening
    the middle part of the afternoon
    eve, even, evening, eventide
    the latter part of the day (the period of decreasing daylight from late afternoon until nightfall)
    any night of the week except Saturday or Sunday
    week from Monday
    a time period of a week or more
    rag, rag week
    a week at British universities during which side-shows and processions of floats are organized to raise money for charities
    Christian year, church year
    the year in the ecclesiastical calendar; especially feast days and special seasons
    Revolutionary calendar month
    a month in the Revolutionary calendar
    Holy Week, Passion Week
    the week before Easter
    Holy Year
    (Roman Catholic Church) a period of remission from sin (usually granted every 25 years)
    New Year
    the calendar year just begun
    the season of Michaelmas
    the season of Lammas
    the Easter season
    the season of Epiphany
    the season of All Saints' Day
    Christmas, Christmastide, Christmastime, Noel, Yule, Yuletide
    period extending from Dec. 24 to Jan. 6
    anomalistic year
    time of the earth's revolution from perihelion to perihelion again; 365 days and 6 hr and 13 min and 53.1 sec
    365 days, common year
    a year that is not a leap year
    366 days, bissextile year, intercalary year, leap year
    in the Gregorian calendar: any year divisible by 4 except centenary years divisible by 400
    off year
    a year in which no major political elections are held
    off year
    a year in which productivity is low or inferior
    calendar year, civil year
    the year (reckoned from January 1 to December 31) according to Gregorian calendar
    astronomical year, equinoctial year, solar year, tropical year
    the time for the earth to make one revolution around the sun, measured between two vernal equinoxes
    lunar year
    a period of 12 lunar months
    financial year, fiscal year
    any accounting period of 12 months
    academic year, school year
    the period of time each year when the school is open and people are studying
    (Latin) year
    the 15th century in Italian art and literature
    twentieth century
    the century from 1901 to 2000
    new moon, new phase of the moon
    the phase in which the moon is in conjunction with sun and is invisible or appears as a narrow waxing crescent
    the time at which the Moon is at first or last quarter when half its face is illuminated
    full, full moon, full phase of the moon, full-of-the-moon
    the time when the Moon is fully illuminated
    lunar day
    the period of time taken for the moon to make one full rotation on its axis (about 27.3 sidereal days)
    sidereal year
    the time for the earth to make one complete revolution around the sun, relative to the fixed stars
    Gregorian calendar month
    a month in the Gregorian calendar
    Jewish calendar month
    a month in the Jewish calendar
    Islamic calendar month
    any lunar month in the Muslim calendar
    Hindu calendar month
    any lunisolar month in the Hindu calendar
    wedding night
    the night after the wedding when bride and groom sleep together
    (law) a time period after which suits cannot be brought
    prison term, sentence, time
    the period of time a prisoner is imprisoned
    academic session, academic term, school term, session
    the time during which a school holds classes
    first trimester
    time period extending from the first day of the last menstrual period through 12 weeks of gestation
    second trimester
    time period extending from the 13th to the 27th week of gestation
    third trimester
    time period extending from the 28th week of gestation until delivery
    extra innings
    overtime play until one team is ahead at the end of an inning; e.g. baseball
    overtime period
    a period of overtime play to resolve a tie; e.g. basketball
    overtime play in order to break a tie; e.g. tennis and soccer
    sudden death
    (sports) overtime in which play is stopped as soon as one contestant scores; e.g. football and golf
    autumn, fall
    the season when the leaves fall from the trees
    spring, springtime
    the season of growth
    summer, summertime
    the warmest season of the year; in the northern hemisphere it extends from the summer solstice to the autumnal equinox
    winter, wintertime
    the coldest season of the year; in the northern hemisphere it extends from the winter solstice to the vernal equinox
    growing season
    the season during which a crop grows best
    the time during which seeds should be planted
    the time or season when sheep are sheared
    holiday season
    a time when many people take holidays
    high season, peak season
    the season when travel is most active and rates are highest
    the season when travel is least active and rates are lowest
    rainy season
    one of the two seasons in tropical climates
    dry season
    one of the two seasons in tropical climates
    a period prior to the beginning of the regular season which is devoted to training and preparation
    baseball season
    the season when baseball is played
    basketball season
    the season when basketball is played
    exhibition season
    the time before the regular games begin when football or baseball teams play practice games
    fishing season
    the season during which it is legal to catch fish
    football season
    the season when football is played
    hockey season
    the season when hockey is played
    hunting season
    the season during which it is legal to kill a particular species
    social season
    the season for major social events
    theatrical season
    the season when new plays are produced
    the season including the four Sundays preceding Christmas
    immediately preceding Lent
    Lent, Lententide
    a period of 40 weekdays from Ash Wednesday to Holy Saturday
    Whitsun, Whitsuntide, Whitweek
    Christian holiday; the week beginning on Whitsunday (especially the first 3 days)
    month of Sundays
    a time perceived as long
    aeon, eon
    an immeasurably long period of time
    blue moon
    a long time
    year dot
    as long ago as anyone can remember
    a short time
    bout, patch, piece, spell, while
    a period of indeterminate length (usually short) marked by some action or condition
    bit, minute, mo, moment, second
    an indefinitely short time
    something transitory; lasting a day
    an era of existence or influence
    year of grace
    any year of the Christian era
    the year 2000 in the Gregorian calendar
    any distinct period in history or in a person's life
    age, historic period
    an era of history having some distinctive feature
    modern era
    the present or recent times
    reign of terror
    any period of brutal suppression thought to resemble the Reign of Terror in France
    press run, print run
    the period that presses run to produce an issue of a newspaper
    (computer science) the length of time it takes to execute a software program
    space age
    the age beginning with the first space travel; from 1957 to the present
    beauty sleep
    sleep before midnight
    (pathology) the phase in the development of an infection between the time a pathogen enters the body and the time the first symptoms appear
    fertile period, fertile phase
    the time in the menstrual cycle when fertilization is most likely to be possible (7 days before to 7 days after ovulation)
    menstrual phase
    the phase of the menstrual cycle during which the lining of the uterus is shed (the first day of menstrual flow is considered day 1 of the menstrual cycle)
    an annual phase of heightened sexual excitement in the males of certain large mammals (especially elephants); is associated with discharge from a gland between the eye and ear
    luteal phase, secretory phase
    the second half of the menstrual cycle after ovulation; the corpus luteum secretes progesterone which prepares the endometrium for the implantation of an embryo; if fertilization does not occur then menstrual flow begins
    a stage of technological development or innovation
    apogee, culmination
    a final climactic stage
    any time of new development
    incumbency, tenure, term of office
    the term during which some position is held
    golden age
    a time period when some activity or skill was at its peak
    the duration of a monarch's or government's power
    safe period
    that time during a woman's menstrual cycle during which conception is least likely to occur (usually immediately before of after menstruation)
    shibah, shiva, shivah
    (Judaism) a period of seven days of mourning after the death of close relative
    a trial period during which an offender has time to redeem himself or herself
    a trial period during which your character and abilities are tested to see whether you are suitable for work or for membership
    type of:
    fundamental measure, fundamental quantity
    one of the four quantities that are the basis of systems of measurement
  2. noun
    the interval taken to complete one cycle of a regularly repeating phenomenon
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    orbit period
    the time it takes to complete one full orbit around a celestial body
    type of:
    interval, time interval
    a definite length of time marked off by two instants
  3. noun
    a unit of geological time during which a system of rocks formed
    synonyms: geological period
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    Quaternary period
    last 2 million years
    Tertiary period
    from 63 million to 2 million years ago
    Cretaceous period
    from 135 million to 63 million years ago; end of the age of reptiles; appearance of modern insects and flowering plants
    Jurassic period
    from 190 million to 135 million years ago; dinosaurs; conifers
    Triassic period
    from 230 million to 190 million years ago; dinosaurs, marine reptiles; volcanic activity
    Permian period
    from 280 million to 230 million years ago; reptiles
    Carboniferous period
    from 345 million to 280 million years ago
    Upper Carboniferous period
    from 310 million to 280 million years ago; warm climate; swampy land
    Lower Carboniferous period
    from 345 million to 310 million years ago; increase of land areas; primitive ammonites; winged insects
    Devonian period
    from 405 million to 345 million years ago; preponderance of fishes and appearance of amphibians and ammonites
    Silurian period
    from 425 million to 405 million years ago; first air-breathing animals
    Ordovician period
    from 500 million to 425 million years ago; conodonts and ostracods and algae and seaweeds
    Cambrian period
    from 544 million to about 500 million years ago; marine invertebrates
    glacial epoch, glacial period, ice age
    any period of time during which glaciers covered a large part of the earth's surface
    type of:
    geologic time, geological time
    the time of the physical formation and development of the earth (especially prior to human history)
  4. noun
    one of the divisions of a school day
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    type of:
    period of time, time period
    an amount of time
  5. noun
    (ice hockey) one of three divisions into which play is divided in hockey games
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    type of:
    division, part, section
    one of the portions into which something is regarded as divided and which together constitute a whole
  6. noun
    the monthly discharge of blood from the uterus of nonpregnant women from puberty to menopause
    synonyms: catamenia, flow, menses, menstruation, menstruum
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    hypermenorrhea, menorrhagia
    abnormally heavy or prolonged menstruation; can be a symptom of uterine tumors and can lead to anemia if prolonged
    abnormally light or infrequent menstruation
    type of:
    discharge, emission, expelling
    any of several bodily processes by which substances go out of the body
  7. noun
    a punctuation mark (.) placed at the end of a declarative sentence to indicate a full stop or after abbreviations
    “in England they call a period a stop”
    synonyms: full point, full stop, point, stop
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    suspension point
    (usually plural) one of a series of points indicating that something has been omitted or that the sentence is incomplete
    type of:
    punctuation, punctuation mark
    the marks used to clarify meaning by indicating separation of words into sentences and clauses and phrases
  8. noun
    the end or completion of something
    “death put a period to his endeavors”
    “a change soon put a period to my tranquility”
    see moresee less
    type of:
    end, ending
    the point in time at which something ends
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