1) Feature of viola music 2) Middle C sign 3) Symbol on viola sheet music 4) Viola staff starter 
In music, an alto clef is the counter-tenor clef, or the C clef, placed so that the two strokes include the middle line of the staff.
[n] - a clef that puts middle C on the third line of a staff
viola clef noun a clef that puts middle C on the third line of a staff
a sign locating middle C on the third line of the staff. Also calledSee illus. under