This is an article specifically about DMX Termination. For basic DMX information, see [[DMX]].
A DMX terminator is a device that uses a resistor (and sometimes other electronics for UI purposes) to stop the flow of the DMX signal so as to eliminate certain problems that will occur otherwise.
A DMX Terminator plugs into the last DMX device's DMX output jack. Using a DMX Terminator improves signal reliability by preventing reflections and reducing ringing. Some DMX terminators feature an LED that indicates when strong DMX signal is on the line. Some terminators also incorporate transient absorbing diodes to suppress spikes that can appear on the control cable during electrical storms. Radio frequency interference (RFI) is bypassed to chassis ground via the .001uF capacitance of the Tranzorb diode.
A home-made version of a terminator could simply be a resistor connecting pins 2 and 3 in a male 3- or 5-pin XLR shell.
More in-depth information on terminators and why/ how to use them can be found in this essay, and easy DIY terminator instructions can be found here.