alto clef

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The C clef positioned to indicate that the third line from the bottom of a staff represents the pitch of middle C.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun music A type of C-clef when placed on the third line of the staff in musical notation.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a clef that puts middle C on the third line of a staff