sleeper

Sleeper is a term with several distinct meanings across everyday language, transportation, and infrastructure. In ordinary use, a sleeper can simply be someone who is asleep. In transport, a sleeper refers to a sleeping compartment or vehicle used for overnight travel—such as a sleeper car on long-distance trains or a sleeper train dedicated to overnight journeys. In rail infrastructure, a sleeper (tie) is the rectangular support that holds rails in place and maintains track gauge, usually made of wood, concrete, or steel.

In media and culture, Sleeper has been used as a title for various works, most famously the 1973 science fiction comedy film Sleeper directed by Woody Allen about a man who awakens in a future society. The name is also adopted by artists and groups as a moniker or project title in different countries.

In espionage and intelligence contexts, a sleeper agent or sleeper cell is a spy who is covertly embedded within a target country, remaining dormant for an extended period and activated to carry out a prearranged mission.

In popular culture and sports, sleeper refers to someone or something that remains undervalued or unnoticed but has potential to perform well: a sleeper pick in a draft, or a sleeper hit—a work that achieves unexpected success after release.