What does "Large Group" vs "Small Group" mean?

Hello :)

I'm not sure if this is just a thing on the Terf-trans alliance sub, but I've seen some discussion on a different classification system other than AGP vs HSTS that I've been having a hard time understanding, so I guess I wanted to post this hoping maybe people could tell me what it means? I saw some people say that "small group" people are people without dysphoria but are naturally more like the opposite sex, but don't have external gender non-conformity? Or something like that? Idk

I guess I was just wondering if anyone else knew about it?