that is the question .... There are three different rotations; spins, rolls and loops. The only difference is the axis of rotation. A spin is where the board stays dangling downwards at the water and you pirouette upright around the body or vertical axis. A roll is a rotation with the legs tucked up a bit and you roll pretty much around the axis in line with the kite lines. The roll is by far the most common form of rotation. A loop is more of an end over end rotation where the board and body become inverted mid rotation. These are most rare and are by far the most difficult of the three rotational jumps.

The spin was one of the first ever rotational jumps and used to be performed unhooked which made it look pretty dangly and awkward. You can see Elliot Leboe, Robby Naish and Lou Wainman doing spins in the earliest videos back in 2000/01. A genuine trick called a "rewind" was also started from unhooked spinning, whereas the rider would spin one way and then "rewind" by spinning back the other way to land The roll came about by being hooked in and tucking the legs up, the plane of rotation became a little more towards the horizontal, about 45 degrees actually in most cases. Rolls are easy and great fun to add simple grabs like tail, tindy, Indy, Slob, Nose, Method etc

The loop is a physically exerted and conscious effort to roll like a summersault whereas the board comes up close to the lines on the way around. Some people extend out as they go over the top to accentuate the inversion. It is by far the hardest to land as it is difficult not to become disoriented during the move for landings. It also takes a fair amount of physical exertion to get into the rotation around the horizontal plane. Hope this helps!