The DMX terminator plug is attached to the back of your moving light or dimmer to properly terminate the DMX512 line from the lighting controller. This can solve a few problems for you. If your lighting malfunctions then it is possible that the last device connected to your controller is not terminated. The DMX 512 specs says that the last device in the chain must be terminated to prevent signal errors from occurring.
NC3MX – NEUTRIK 3 Pole Cable Connector, Male