You ought to have seen it before in the glossary, as this term has come up at least once before — and I would refer you to the earlier question(s) for a much fuller discussion of all the possible meanings of this term.

The trouble is, different writers use it differently, and hence the EN term needed varies quite a lot; you may need to look for other clues in your wider text in order to try and find out what your particular writer intended it to mean!