A sleeper cell is a group of operatives, spies, or terrorists who live in secret among a targeted community, waiting for instructions or an opportunity to act. Sleeper cells are often used in espionage and terrorism, and their members work under cover in an area until they are sent into action. In espionage, a sleeper agent is a spy who is placed in a target country or organization not to undertake an immediate mission, but instead to act as a potential asset if activated. Sleeper agents may also work in groups of a clandestine cell system with other agents. The term "sleeper cell" can also refer to a group of people who remain dormant in a community until activated, by a prearranged signal, to perform acts of espionage, sabotage, or terrorism.