Domain

Domain is the sphere of knowledge that defines a set of common requirements, terminology, and functionality for any program or initiative solving a problem.

Definitions

According to the BABOK Guide (3rd edition),

Domain. The sphere of knowledge that defines a set of common requirements, terminology, and functionality for any program or initiative solving a problem.

According to the Marketing Communications by Fill (5th edition),

Domain. An area, field or sphere of function undertaken by organizations. There are four main elements: population, territory, roles and issues.