"glass bow" usually refers to a composite bow made from thin laminations (strips) of wood between a back and belly lamination of unidirectional fiberglass (fibers run from tip to tip, only).
Lee's bow, as he describes in the preceding pages, is composed of a dark wood handle or "riser", two or more light wood laminations running from tip to tip, and black fiberglass laminations running from tip to tip on the back and belly.