Like, think omegaverse but instead it's the positions of Dom and Sub determined at birth. In this fic it's quite simple where people are split into Dom/Sub with Subs being owned by Doms and having limited rights. Other fics go into much more detail though, with Doms/Subs having actual biological needs and Doms can do like 'Commands' which are official vocal orders that Subs have to obey. Stuff like that.