The tag alias #76285 tailbutt -> side_hips is pending approval.
Reason: "side hips" is a more intuitive name than tailbutt for what the definition of the tag is. Notably, in topic #42705, the creator of the tailbutt tag explains what it means saying:
"note that the hips are always to the side of the tail, at most slightly converging to indent the tail rather than completely merging into one "hip" piece."
A direct link to where this is said; Only works on certain browsers
side_hips is currently on 17 posts but doesn't have an agreed upon meaning, as can be seen in the inconsistency of the content in the posts that it is used on.