In
espionage jargon, a
mole (also called a
penetration agent,
deep cover agent, or
sleeper agent) is a long-term
spy (espionage agent) who is recruited before he or she has access to secret intelligence, and subsequently works his or her way into the target organization. However it is popularly used to mean any long-term clandestine spy or
informant within an organization, whether government or private.