String instruments are pitched instruments and utilize the two basic types of note heads: solid and hollow.
Non-pitched instruments, such as many percussion instruments (drums), utilize varied note head symbols including slashes, X’s and triangles. Contemporary composers have even invented other types of note heads.
Notes also serve to represent exact pitch locations too. However, regardless of the pitch, a note’s precise rhythmic definition remains intact.
Note heads most often combine with Stems in order to form notes.
Solid Note Heads always need to have a stem in order to become a note.
Hollow Note Heads can either have a stem or stand alone as a note.