The word commutator is sometimes mistakenly used in place of the general term slip ring. A commutator is a specialized slip ring typically used on Direct Current motors and electrical generators to transfer electrical power between the stationary housing and the rotating armature with the added purpose of reversing the electrical current direction.
A commutator ring is made of insulated metal segments unlike the solid metal ring of a slip ring. Electrical brushes (contacts) rub on this rotating ring to make the electrical connection. These ring segments are wired to act as a rotary switch in order to reverse the electrical current. In a DC motor this switching reverses the magnetic field to keep the motor turning. In a generator the switching changes alternating current into current flowing in one direction (DC).