Source : Webster's Revised Unabridged Dictionary (1913)

Sixty-fourth \Six`ty-fourth"\, a.
   Constituting or being one of sixty-four equal parts into
   which a thing is divided.

   {Sixty-fourth note} (Mus.), the sixty-fourth part of a whole
      note; a hemi-demi-semiquaver.

Source : WordNet®

sixty-fourth note
     n : a musical note having the time value of a sixty-fourth of a
         whole note [syn: {hemidemisemiquaver}]