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. Interaction is action that occurs between two or more entities, generally used in philosophy and the sciences. It may refer to: InterAction is an alliance of more than 190 international NGOs partnering to eliminate extreme poverty, safeguard a sustainable planet and promote peace. INTERACTION definition: 1. an occasion when two or more people or things communicate with or react to each other: 2. an…. Learn more. INTERACTION definition: reciprocal action, effect, or influence. See examples of interaction used in a sentence. INTERACTION meaning: 1. an occasion when two or more people or things communicate with or react to each other: 2. an…. Learn more. The meaning of INTERACTION is mutual or reciprocal action or influence. How to use interaction in a sentence. 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. 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. (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.