a trailer. A 5th wheel is much more light duty than a gooseneck ball setup. The ball is much less expensive to install than buying a 5th wheel hitch. If you're a farmer with 3 or 4 different trucks (flatbed, pickup, etc), and you want the ability to move your trailer with whatever truck you happen to be in, installing a ball in the bed is a much cheaper option (with much heavier duty capabilities) than a 5th wheel.

The vast majority of trailers that have a 5th wheel hitch are camper trailers. Everything else for the most part is a gooseneck. Larger trailers with a 5th wheel hitch need a semi to pull them.