The word key has several uses:

• A key (lock) as a physical object (tool) used to manipulate a lock.
• A key (music) forms a property of a piece of music: see also key signature.
• A key (cryptography) consists of a piece of information, usually kept secret, used to customise ciphers.
• A key (instrument) comprises a moving part of a musical instrument.
• Key (company), a Japanese firm, makes ren'ai video games.
• In database design, keys refer to unique values in database rows. See primary key and related articles.
• A telegraph key serves to send Morse code.
• Typewriters and computer keyboards have buttons called keys used for the input of text or commands.
• A key (map) consists of the section of a map or other document that explains the symbols used elsewhere on the document.
• A key (art) features in painting and photography.
• A key frame constitutes a frame or cell in animation which serves as a guide for the other frames, or inbetweens. Usually the key framer is a more prominent artist than inbetweeners.
• An identification key can help to identify species.
• The word key or cay may refer to an island, especially in the Caribbean Sea.
• The Florida Keys consist of a chain of islands off the coast of Florida.
• A skate key functions as a tool in the adjusting of roller skates.
• Keying (graphics) involves compositing two or more frames in video editing.
• Keying (vandalism) involves using something metallic, such as a latch-key, in order to scratch something (often something of perceived value) such as a car, thereby vandalizing it.
• The House of Keys (also knowns as "The Keys") operates as part of the Tynwald - the parliament of the Isle of Man
• The word "key" has a homophone: quay.
• The word Key can refer to an English surname, as in Francis Scott Key.