Post-credits scene

A post-credits scene appears after or during the closing credits of a movie. They are mostly used to amuse the audience or tell them that a sequel is coming soon.
The first post-credits scene is usually thought to be in 1903's "The Great Train Robbery", in which the leader of the outlaw aims his gun at the audience and fires it. They gained popularity during the 1980s. An example is "Ferris Bueller's Day Off", in which the title character tells the audience to leave the theatre.
Marvel Cinematic Universe movies are famous for these scenes, in which they usually tell the audience that a movie based on another Marvel hero is coming.