I've seen rather gross misuse of the prolapse tag. Prolapse means for something, mainly organs, to slip or fall out of place. I tend to see this tag thrown on pretty much anything that has large genitalia.

Here are some examples of Prolapse
https://e621.net/post/show/360174 - anal
https://e621.net/post/show/257577 - vaginal

These are not prolapse
https://e621.net/post/show/344721 - vaginal
https://e621.net/post/show/214959 - anal

In such cases the tags that should be considered are puffy_anus, plump_labia and fat_mons. The latter which really needs to be used and gets mistaken for plump_labia.