Hunters or hunt seat is a discipline, two point is a position. In hunt seat riding, you might ride in a full seat, a three point contact or two point contact, depending on the circumstances.
Hunters or hunt seat has two main sub divisions -
Hunt seat equitation, where the rider is judged
Hunters, either under saddle or over fences, where the horse's style, manners and suitablity are judged.
Jumpers are something else entirely, judged objectively on jumping faults and speed.
Hunter/Jumper is a odd regional term that means the same thing as Hunter Over Fences. It's confusing, as hunters and jumpers are very different disciplines judged on entirely different criteria, but it's a common term in certain areas and at breed shows with a lot of Hunter flat (under saddle/not over fences) classes.