1. The independent variable used to express a function. Note: Examples of domains are time, frequency, and space. 2. In distributed networks, all the hardware and software under the control of a specified set of one or more host processors. 3. A unique context (e.g., access control parameters) in which a program is operating; in effect, the set of objects a subject has the privilege to access. 4. The set of objects that a subject has the ability to access.