A stimulator is a device which sends signals into another device that make that device think it is getting the kinds of inputs it was designed to receive even though the information it is receiving is simulated.

An example of a stimulator would be a device which sends little pulses into the front end of a radar that look to the radar like targets but really are not.  This kind of a device tests the radar and the interfaces of the radar to the data system without actually deploying and operating the radar transmitter, at least at full power.

It is a very powerful way of increasing the fidelity of a controlled test environment.  But it tends to be expensive because all the stimulators are custom designs usually.  It is almost the only way to get ''end to end''
testing at a high level of ''fidelity''
in a complex system without actually deploying the system.  --RaySchneider