A short glossary or definition page is enough to rank and index when it fully and best answers a genuine definitional query and carries some unique value, and it falls short when it is a thin echo of countless identical entries. The threshold is not length, it is whether the page does the job better than what already exists. A 150-word definition can rank if it is the clearest, most complete, best-structured answer a searcher could land on. The same 150 words fail when they restate the dictionary and add nothing.
The pivot is fully-answers-with-some-gain versus thin-duplicate. A short page earns its place when it nails the exact thing the searcher came for: a precise definition, a clean example, the one distinction people get wrong, a quick note on when the term applies. That is unique value, and it is what separates a page worth indexing from filler. The page that loses is the one indistinguishable from a hundred others, where the definition is generic, the structure is a single unstyled paragraph, and a reader gains nothing they could not get from the first result already ranking.
So neither extreme holds. It is not true that short definition pages cannot rank, plenty of them sit at the top of definitional queries because they answer cleanly and completely. It is also not true that every term in your space deserves its own page. A term only warrants a standalone page when it draws genuine search demand and you can answer it more completely or more clearly than the field, or fold it into a broader page where it belongs as a section. Demand plus a real gain is the test, not the existence of the word.
Before you publish a glossary page, hold it against the results already ranking for that term and ask what a searcher gains here that they cannot get there. If the answer is a clearer definition, a sharper example, or a distinction nobody else surfaces, make the page complete and distinct and ship it. If the honest answer is nothing, do not make the page, because a thin duplicate dilutes your site rather than building it.