Can we then change the term then from "niche market" to "specialized user group" or something. Or whatever fits your elite marketing and advertising bred tongue. We all know what we are talking about here -- that the graph represents a small user group consisting of incoming freshmen in a single university.
I think it's more productive to stay focused on the main topic, rather than sidetracking and having an intellectual competition on word definitions. Thumping dictionaries only shows how inflexible you are in dealing with people outside of your profession.