key signature noun
: the sharps or flats placed after a clef in music to indicate the key
First Known Use of KEY SIGNATURE
key signature noun (Concise Encyclopedia)
In music, the sharps or flats placed on the staff to indicate the key for a composition or a section. Placement of the symbols on lines and spaces indicates which notes are to be altered by the sharps or flats; for example, a sharp on the top line of the treble clef governs every F on the staff and indicates the key of G major or E minor. Each set of major and minor keys is designated with a particular grouping of sharps or flats.
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