A grace note is a kind of musical notation used to denote several kinds of musical ornaments.
"In notation a grace note is distinguished from a regular note by print size. A grace note is indicated by printing a note that is much smaller than a regular note, sometimes with a slash through the note stem (if two or more grace notes, there might be a slash through the note stem of the first note but not the subsequent grace note). The presence or absence of a slash through a note stem is often interpreted to indicate the intention of an acciacatura or an appoggiatura, respectively.
The works of some composers, especially Frédéric Chopin, may contain long series of notes printed in the small type reserved for grace notes simply to show that the amount of time to be taken up by those notes as a whole unit is a subjective matter to be decided by the performer. Such a group of small printed notes may or may not have an accompanying principal note, and so may or may not be considered as grace notes in analysis."