The rotor is the rotating part of a machine. In electric motors or generators, the term "rotor" refers to the entire linearly rotating part of the machine.
The stator, on the other hand, refers to the stationary, non-moving part of a machine. Alternative terms for "rotor" and "stator" are "runner" and "stand." Depending on the motor's design and type, the rotor or stator may be constructed as a permanent magnet or copper winding.