Key (music)

In music theory, the key of a piece usually refers to the tonic note and chord, which gives a subjective sense of arrival and rest. Other notes and chords in the piece create varying degrees of tension, resolved when the tonic note and/or chord returns. The key may be major or minor, although major is assumed in a phrase like “this piece is in C. ” Popular songs are usually in a key, and so is classical music during the common practice period, about 1650–1900.