domain

A geographic area owned or controlled by a single person or organization.

The king ruled his domain harshly.

Bears and other ferocious beasts resented man's intrusion into their domain; so, too, did the Blackfoot Indians and other tribes, whose savage hostility was a constant menace to the lives of the toiling engineers.

A field or sphere of activity, influence or expertise.

Dealing with complaints isn't really my domain: get in touch with customer services.

His domain is English history.

A group of related items, topics, or subjects.

Some of the most beautiful and thus appealing physical theories, including quantum electrodynamics and quantum gravity, have been dogged for decades by infinities that erupt when theorists try to prod their calculations into new domains. Getting rid of these nagging infinities has probably occupied far more effort than was spent in originating the theories.

The set of input (argument) values for which a function is defined.

The set of input (argument) values for which a function is defined.