Mission-essential functions

U.S. government
Mission essential functions (MEF) are

"the limited set of department- and agency-level government functions that must be continued throughout or resumed rapidly after a disruption of normal activities."

U.S. military
Mission essential functions (MEF) are

"those organizational activities that must be performed under all circumstances to achieve DoD component missions or responsibilities, as determined by the appropriate functional commander or civilian equivalent. Failure to perform or sustain these functions would significantly affect DoD's ability to provide vital services or exercise authority, direction, and control.""