According to PrestigeTime.com, the term bezel refers to the ring located on the top side of the watch case. The bezel often has time increments marked on it. Movable bezels can serve other functions, such as tracking elapsed time. However, bezels can also be fixed, meaning they don't move.
A bezel that can move is called either a uni-direction bezel or a bi-directional rotating bezel, says PrestigeTime.com. The former can only rotate in one direction, whereas the latter can rotate both clockwise and counter-clockwise. Bezels may be adorned with jewels, or they may be free of adornment, depending on the watch.