From Longman Dictionary of Contemporary Englishbass clefbass clef /ˌbeɪs ˈklef/ noun [countable] APMa sign ( ) at the beginning of a line of written music that shows that the top line of the stave is the A below middle C
Examples from the Corpus
bass clef• Formerly, notes written in the bass clef were written a fourth lower than the required pitch instead of a fifth higher.• The bass clef is used for the lower parts of the compass, the tenor for the higher. 