Musica ficta

A medieval term describing all those notes in use at the time that are not to be found on the Guidonian hand. This term is also used to describe those notes that a modern performer would change by a semitone when playing Medieval music; these alterations are not written into the manuscript. (1) a note lying outside of Guido of Arezzo's hexachordal system including accidentals other than B flat and pitches from outside of the gamut. (2) accidentals added by modern-day editors. They often appear above the note in question.