What does staff music meen?

Grand staff?

When music on two staves is joined by a brace, or is intended to be played at once by a single performer (usually a keyboard instrument or the harp), a great stave (British English) or grand staff (American English) is created. Typically, the upper staff uses a treble clef and the lower staff has a bass clef.

I'm not sure but I used to take a piano lesson. Staff is the lines on the music sheet.