grace note

A small note, often used to show an ornament or embellishment, that is not counted towards the number of beats in the bar; when performed, it steals from the duration of either the preceding or the following rhythmic notes. Also known as arhythmic notes. In common practice, a grace note with a slashed stem is an acciaccatura, which is to be played as quickly as possible, either immediately before or at the rhythmic position of the note or chord that follows it; a grace note with an unslashed stem is an appoggiatura, which is played as half of the written duration of the note or chord that follows it.