succinct, comprehensive statement of purpose of an agency, program, subprogram, or project that is consistent with a vision statement.
[d]escription prepared and endorsed by members of the organization that answers these questions: What do we do? For whom do we do it? How do we go about it? Used as a guide for making decisions in projects.
[a] short sentence or paragraph that describes the organization's essential task (or tasks) and purpose — a clear statement of the action to be taken and the reason for doing so. The mission statement contains the elements of who, what, when, where, and why, but seldom specifies how.
↑Office of Counterintelligence (DXC), Defense CI & HUMINT Center, Defense Intelligence Agency, "Terms and Definitions of Interest for DoD Counterintelligence Professional," at GL-118 (May 2, 2011) (full-text).