If you interact with someone — by talking, looking, sharing, or engaging in any kind of action that involves the two of you — you can be said to have had an interaction with that person.

Interaction comes from Latin inter meaning "between," and ago meaning "to do" or "to act" — any “action between” is considered an interaction, like the interaction between a teacher and a student, two countries, or even baking soda and vinegar (boom!).

Definitions of interaction
  1. noun
    a mutual or reciprocal action; interacting
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    reciprocal action and reaction
    close interaction
    give-and-take, interchange, reciprocation
    mutual interaction; the activity of reciprocating or exchanging (especially information)
    contact with something dangerous or undesirable
    eye contact
    contact that occurs when two people look directly at each other
    contact established between applicants and prospective employees
    mutual exchange of commercial or other privileges
    cross-fertilisation, cross-fertilization
    interchange between different cultures or different ways of thinking that is mutually productive and beneficial
    dealings, traffic
    social or verbal interchange (usually followed by `with')
    type of:
    something done (usually as opposed to something said)
  2. noun
    (physics) the transfer of energy between elementary particles or between an elementary particle and a field or between fields; mediated by gauge bosons
    synonyms: fundamental interaction
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    electromagnetic interaction
    an interaction between charged elementary particles that is intermediate in strength between the strong and weak interactions; mediated by photons
    gravitational interaction
    a weak interaction between particles that results from their mass; mediated by gravitons
    color force, strong force, strong interaction
    (physics) the interaction that binds protons and neutrons together in the nuclei of atoms; mediated by gluons
    weak force, weak interaction
    (physics) an interaction between elementary particles involving neutrinos or antineutrinos that is responsible for certain kinds of radioactive decay; mediated by intermediate vector bosons
    type of:
    physical phenomenon
    a natural phenomenon involving the physical properties of matter and energy
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