Your birthday is the day of your birth! It’s the yearly anniversary that marks the day you were born. Not everyone celebrates, but a birthday is a good excuse for a party and cake.

You can use birthday both to refer to the specific day of a baby's birth, and the annual marking of that day throughout the years that follow. Sometimes people talk about the birthday of a country, group, or even a building: "It's the art museum's fiftieth birthday next year." The Old English byrddæg originally referred to the celebration of a king or saint's birth, but over the years it was extended to include everyone.

Definitions of birthday
  1. noun
    the date on which a person was born
    synonyms: natal day
    see moresee less
    type of:
    date, day of the month
    the specified day of the month
  2. noun
    an anniversary of the day on which a person was born (or the celebration of it)
    see moresee less
    type of:
    anniversary, day of remembrance
    the date on which an event occurred in some previous year (or the celebration of it)
Word Family

Test prep from the experts

Boost your test score with programs developed by’s experts.

  • Proven methods: Learn faster, remember longer with our scientific approach.
  • Personalized plan: We customize your experience to maximize your learning.
  • Strategic studying: Focus on the words that are most crucial for success.


  • Number of words: 500+
  • Duration: 8 weeks or less
  • Time: 1 hour / week


  • Number of words: 500+
  • Duration: 10 weeks or less
  • Time: 1 hour / week


  • Number of words: 700+
  • Duration: 10 weeks
  • Time: 1 hour / week