In ethology, territory is the sociographical area that an animal of a particular species consistently defends against conspecifics (or, occasionally, animals of other species). Animals that defend territories in this way are referred to as territorial.
Territoriality is only shown by a minority of species. More commonly, an individual or a group of animals has an area that it habitually uses but does not necessarily defend; this is called the home range. The home ranges of different groups of animals often overlap, or in the overlap areas, the groups tend to avoid each other rather than seeking to expel each other. Within the home range there may be a core area that no other individual group uses, but, again, this is as a result of avoidance.
The ultimate function of animals inhabiting and defending a territory is to increase the individual fitness or inclusive fitness of the animals expressing the behaviour. Fitness in this biological sense relates to the ability of an animal to survive and raise young. The proximate functions of territory defense vary. For some animals, the reason for such protective behaviour is to acquire and protect food sources, nesting sites, mating areas, or to attract a mate.