interaction (countable and uncountable, plural interactions) The situation or occurrence in which two or more things act upon one another to produce an effect; the effect resulting from such a situation or occurrence. (General Physics) physics the transfer of energy between elementary particles, between a particle and a field, or between fields. See strong interaction, electromagnetic interaction, fundamental interaction, gravitational interaction, weak interaction, electroweak interaction. 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 brings together U.S.-based global NGOs to navigate change, coordinate action, and strengthen collective impact in a rapidly evolving humanitarian and development landscape. The meaning of INTERACTION is mutual or reciprocal action or influence. How to use interaction in a sentence. InterAction mobilizes over 170 NGOs to advocate for policies and solutions that advance the lives of those in the poorest and most marginalized places. This disambiguation page lists articles associated with the title Interaction. If an internal link incorrectly led you here, you may wish to change the link to point directly to the intended article. INTERACTION definition: reciprocal action, effect, or influence. See examples of interaction used in a sentence. Communicating & keeping in touch (Definition of interaction from the Cambridge Advanced Learner's Dictionary & Thesaurus © Cambridge University Press) INTERACTION definition: 1. an occasion when two or more people or things communicate with or react to each other: 2. an…. Learn more.