Key is a musical term used to tell the tonal system in which a musical composition is written. The key includes all of the tones of a particular scale and all of the chords made from those tones. The first note of a scale is called the keynote, or tonic, and the key gets its name from that first note. The key of C, for example, has as its keynote C, which is the first note of the C scale. Each of the 12 major and 12 minor scales has a keynote.
The term key also means the small finger piece that opens and closes the sound holes on wind instruments. Instruments such as the piano or organ have levers called keys.
