What is The difference between hunter jumper and hunt seat?

A saddle hunter is horse that can carry a large amount of weight over distance. Generally not a 'pretty' horse like a arabian or a fine boned tb. A hack, definition wise, tends to vary. But sometime is referred to a horse who is used for normal riding or a horse who is well trained, calm and 'easy'. To 'hack' can also be to have a short ride. Some equestrians believe it means to do a trail ride but a hack doesn't have to leave the arena. It is just a short, easy ride.