A sphere of knowledge, influence, or activity. The subject area to which the user applies a program is the domain of the software.
A system of abstractions that describes selected aspects of a domain and can be used to solve problems related to that domain;
A cluster of associated objects that are treated as a unit for the purpose of data changes. External references are restricted to one member of the Aggregate, designated as the root. A set of consistency rules applies within the Aggregate's boundaries.