Skinwalker
Skinwalkers are evil sorcerers from Navajo folklore with the ability to turn into animals (or possess animals, its not too clear). The Navajo themselves call them yee naaldlooshii which literally means "by means of it, it goes on all fours".
Pathfinder
In Pathfinder, skinwalkers are a type of beastkin, a sort of Half-Werebeast. Descended from true therianthropes, they have weaker shapeshifting abilities, and are not able to take a completely animal form. The skinwalker is unique in that it is the generic beastkin, not based on any particular animal.
In Pathfinder 2e, beastkin is now a blanket term for all therianthropes.