1. In music, key refers to "key", and "key" is the position of the pitch, that is, the height of the sound. To be more precise, it is the pitch position of the "main tone", which is also the key in music. Call key a scale.

2. It is also the pitch of the tonic (starting tone) of a certain mode. The name of the tonic pitch is the name of the key (tone door) of this mode.