The word cylinder has several meanings.

• For the geometric object, see cylinder (geometry).
• For the engine component, see cylinder (engine).
• In firearms, the cylinder is the rotating device that contains the firing chambers of a revolver.
• The phonograph cylinder was the dominant medium of audio storage from the 1870s to the 1910s, and continued in limited use (such as in the dictaphone) through the mid 20th century.
• A cylinder is also a type of lens and a form of refraction error.
• Also see gas cylinder.