A wetsuit jacket is very similar to a wetsuit top with the only main difference being that the jacket typically has a full zipper which opens completely in the front. This makes it easier to put on and off. Some wetsuit tops, however, are also called wetsuit jackets even if they don’t have a zipper. Its fuzzy. While zippers are great for getting in and out of the jacket, they can be a problem for surfers since they would be lying directly on the zipper while paddling out, it would get messy with the wax getting into the zipper and so on…
You can also choose a wetsuit jacket which has a short zipper just below the neck. This is a great compromise since you can comfortably lay on a surf board, but also have the option to unzip to cool off when you want to.
Another difference between a wetsuit top and a jacket is that the jacket is usually thicker. The thick neoprene will help provide more warmth than a simple top which is thinner. While there are no set rules on this most wetsuit jackets will be around 2 millimeters thick and a top is between .5 and 1.5 millimeters thick.
A wetsuit jacket is much more popular among the divers. Most divers who use them use them in warm water temperatures around 72 degrees. If you add on a long john to it, you are ready for colder water.
If you want to learn more about which wetsuit goes with which water temperature and what are the factors that influence the feeling of cold check this article.