key signature 
noun Music
Any of several combinations of sharps or flats after the clef at the beginning of each stave, indicating the key of a composition.Guidelines for clefs, key signatures, bar-lines, and notes are similarly drawn in....
- For example, the given notated B-flat cornet part has a key signature of one sharp.
- The student soon realizes that key signatures with the resulting sharps or flats are the consequence of a consistent melodic sequence contained within a scale pattern.