1. A pause or break; especially, in a concerto, a pause in the accompaniment to give room for an extended cadenza by the soloist.
2. A hold or pause upon a tone or chord, the length being discretionary with the performer or conductor.
3. The sign placed over or under a note or even a bar to indicate such a hold or pause.
I'm sure I don't need to think of another clue and answer, Ecce...