What is the definition of the musical term key

In music theory, the key of a piece is the group of pitches, or scale that form the basis of a music composition in classical, Western art, and Western pop music.

In music theory, the key of a piece is the group of pitches, or scale that form the basis of a music composition in classical, Western art, and Western pop music. ... Notes and chords other than the tonic in a piece create varying degrees of tension, resolved when the tonic note or chord returns.

Normally it is at the top left, above where the music starts.

Cwealthy young people listening to music under orange tree