A covert operation or undercover operation is a military or police operation involving a covert agent or troops acting under an assumed cover to conceal the identity of the party responsible. Some of the covert operations are also clandestine operations which are performed in secret and meant to stay secret, though many are not.

A cover in foreign, military or police human intelligence or counterintelligence is the ostensible identity and/or role or position in an infiltrated organization assumed by a covert agent during a covert operation.