accidental
n. countablen. a symbol in music that changes a note's pitch for a short time. It tells you to play a note slightly higher or lower than usual for just one part of the song.
n. a sign placed before a note to indicate a temporary departure from the key signature by raising or lowering its pitch. It remains in effect for the duration of the measure in which it appears.
The composer added an accidental to make the melody sound more mysterious.
While the piece is written in G major, the frequent use of accidentals creates a chromatic texture that challenges the performer.
In modern atonal compositions, every note may require an accidental to clarify the intended pitch, as traditional key signatures no longer provide a functional harmonic framework for the performer.
From Middle English accidental, from Anglo-Norman accidentel, Middle French accidentel, accidental, and their source, Late Latin accidēntālis; corresponding to accident + -al.
In music theory, the term refers specifically to sharps, flats, and naturals not indicated in the key signature.