The acciaccatura (Italian: acciaccare, 'to crush') is an ornamental grace note played simultaneously with, or just before, the principal note it is attached to. It is released almost instantaneously. It is sometimes thought of as a shorter, less melodically significant, variant of the long appoggiatura, where the suspension of the principal note is scarcely perceptible, although formally this usage is incorrect. A late Baroque keyboard ornament, it is written using a grace note (often a quaver, or eighth note), with an oblique stroke through the top of the stem.
Whether the note should be played before or on the beat is largely a question of taste and performance practice. Exceptionally, the acciaccatura may be notated in the bar preceding the note to which it is attached, showing it is to be played before the beat. It is usually employed with an emphasis in arpeggiated chord-playing.