To behave means to act in a particular way, especially in a manner that others consider appropriate or acceptable. When your parents remind you to behave at your grandmother's house, they're asking you to use good manners, speak politely, and follow the rules. When a teacher says the class behaved well during the assembly, she means everyone sat quietly and listened respectfully.

The word describes all kinds of actions, not just good ones. A scientist might observe how chemicals behave when mixed together, meaning how they react and what they do. A car that behaves strangely might make odd noises or not accelerate properly. In these cases, behave simply means “to act” or “to function.”

But when someone tells you to behave without any other description, they almost always mean behave well or behave properly. Understanding how to behave in different situations takes practice and attention: you behave differently at a library than at a playground, and differently at a formal dinner than at a backyard barbecue. Learning to read these situations and adjust your behavior accordingly is an important part of growing up.

The related word behavior describes patterns of how someone typically acts. A student with good behavior consistently follows rules and treats others with respect.