To my knowledge, it does not include "glue" in alternative photography.
When we say "gum" it is one of the chemical "gums" like gum arabic, gum
tragacanth, etc.(dozens of them), all of which are saps or exudations.
Carpenters and other mechanics might use the term "gum" to include glue,
but I've never known that to be true in photography. Glues, indeed, have
been used, but they have not been called gums.
Sil Horwitz, FPSA
Technical Editor, PSA Journal
silh@iag.net