A territory is an area of land that belongs to or is controlled by a particular group, government, or animal. When explorers in the 1800s pushed westward across North America, they moved through vast territories that later became states. Before Arizona or Montana were states, they were territories: regions under U.S. government control but not yet organized as full states with all the same rights and representation.

Countries defend their territories, the lands within their borders. A nation's territory includes everything from its cities and farms to its mountains and coastlines. When armies invade another country's territory, they're crossing into land that isn't theirs.

Animals have territories too. A wolf pack claims a territory where it hunts and raises its young, marking the boundaries and defending them from other wolves. Birds, bears, and even house cats establish territories they consider their own space.

The word also describes areas of responsibility or expertise. A salesperson might have a sales territory, a specific region where they work with customers. You might think of your bedroom as your territory, your personal space where you make the rules. When someone says “that's not my territory,” they mean it's outside their area of knowledge or responsibility.