It’s about the joining of the different disciplines, and not particularly a discipline in and of itself. While the best designers have an awareness of the disciplines that surround and overlap theirs, to be considered an experience designer would necessarily require management and coordination between the disciplines to ensure holistic products. This is an essential skill for making the best products, of course, but I would guess this is often a temporary role that designers move into during key points in the design process from a starting point of one of the other disciplines. Without the “raw materials” of the disciplines that make up UX, UX would be empty indeed. Source