The phrase "to act out" means to behave in a way that is not appropriate or acceptable, often by expressing one's emotions through physical actions. This can include things like shouting, hitting, kicking, or other forms of aggression. It may also refer to engaging in self-destructive behavior such as substance abuse, excessive spending, or risky sexual behaviors. In some cases, "to act out" can simply mean expressing emotions through physical movements, like dancing or acting out a scene from a play.