To interact means to communicate with or respond to someone or something. When you interact with your friends at lunch, you talk, laugh, share stories, and react to what they say. When you interact with a video game, you press buttons and the game responds to your actions.

Interaction is a two-way street: both sides affect each other. Reading a book quietly isn't interacting because the book doesn't respond to you. But discussing that book with your teacher is interacting because you exchange ideas back and forth. Scientists study how animals interact with their environments, watching how a beaver's dam-building changes the river and how the river's flow affects where the beaver builds.

The word emphasizes active participation rather than passive observation. You might watch a documentary about space without interacting, but when you visit a science museum with hands-on exhibits, you interact with the displays by touching, experimenting, and seeing immediate results.

People also use interaction as a noun to describe these exchanges: “The interaction between the two characters made the play exciting,” or “My interactions with my grandmother taught me about her childhood.”