Acciaccatura n. : A short grace note, one semitone below the note to which it is prefixed; -- used especially in organ music. Now used as equivalent to the short appoggiatura.

Example:
What exactly is an Acciaccatura, and how do you play one on guitar?

Taxonomy
ornaments, trill, mordent, music, ornamentation, principal note, List of ornaments, appoggiatura, acciaccatura, passaggi, grace notes, mordents, notated music, instruments, jazz, beat, treatises, Venice.

Defination from the web:
acciaccatura (see below), these are almost always quite short, and take their time from the allocation for the ... The acciaccatura (sometimes called short appoggiatura) is perhaps best thought of as a shorter, less melodically significant, variant of the long ...