(from wikepedia)
In music notation, a sixty-fourth note (American or "German" terminology) or hemidemisemiquaver (British or "classical" terminology) is a note played for 1/64 of the duration of a whole note (or semibreve). It lasts half as long as a thirty-second note (or demisemiquaver).

Sixty-fourth notes are notated with a filled in oval note head and a straight note stem with four flags. The stem is drawn to the left of the note head going downward when the note is above or on the middle line of the staff. When the note head is below the middle line the stem is drawn to the right of the note head going upward. Multiple adjacent sixty-fourth notes may have the flags connected with a beam.

A similar, but rarely encountered symbol is the sixty-fourth rest (or hemidemisemiquaver rest, shown on the right of the image) which denotes silence for the same duration as a sixty-fourth note.

Notes shorter than the sixty-fourth note are very rarely used in music, though the hundred twenty-eighth note (otherwise known as the semihemidemisemiquaver or quasihemidemisemiquaver), or even shorter notes, are occasionally found.