alto clef definition by Webster's New World
Webster's New World College Dictionary Copyright © 2010 by Wiley Publishing, Inc., Cleveland, Ohio. Used by arrangement with John Wiley & Sons, Inc.
a C clef on the third line of a staff: used in notation, esp. for the viola
alto clef definition by American Heritage Dictionary
The C clef positioned to indicate that the third line from the bottom of a staff represents the pitch of middle C.