Aggression is hostile or forceful behavior intended to dominate, harm, or intimidate others. When someone shoves another student in the hallway instead of asking them to move, that's physical aggression. When someone repeatedly insults or threatens a classmate, that's verbal aggression.

Aggression goes beyond ordinary conflict or competition. Two basketball players fighting hard for a rebound isn't aggression, but one player deliberately elbowing another in the face is. The key difference is intent: aggressive behavior aims to hurt, control, or frighten someone rather than simply win fairly or stand up for yourself.

In international relations, aggression means one country attacking or invading another without justification. When people study history, they learn how military aggression has led to devastating wars. Nations created organizations like the United Nations partly to prevent aggression between countries.

Psychologists distinguish between different types of aggression. Reactive aggression happens when someone lashes out in anger after being provoked. Proactive aggression is more calculated, like a bully targeting someone weaker to gain social status. Animals also display aggression when defending territory or competing for resources.

The word can also describe behavior that's merely pushy or overly assertive, though this usage is less common. An aggressive salesperson might pressure customers too hard, or an aggressive driver might tailgate and weave through traffic dangerously.