A wheel can only go in one direction at a time because it has a single axis. A caster wheel has a wheel PLUS a mounting system that holds the wheel. There are two kinds of casters, fixed casters, (sometimes also referred to as rigid casters) and swivel casters. Rigid casters are best for things that only need to go forward and backward. Swivel casters rotate 360 degrees and thus can be used to turn objects. The caster wheels we use on our soccer goals are swivel casters.