I think this has been discussed before - several years ago.
Graphemes and morphemes belong to the same 'category': that of small units carrying meaning.
Glyphs are the writable results of merging one or more graphemes, so that the glyph for a certain handshape will also reveal a certain rotation (placement of long axis of hand) and a certain fill (rotation along this long axix).
The symbol for the back of the hand is black (fill), for the palm it is white (no fill), and so on.
But maybe there are conventions for use of these words in connection with Unicode, which would of course be more important than my private houghts ...