EILD can stand for both externally induced lucid dream or electrically induced lucid dream. Originally it was 'electrically', however the device does not have to be electrical. During sleep your senses still monitor the outside world. If they didn't you would be unable to wake up from an alarm clock.
The EILD technique takes advantage of this. You have a device signal you when you enter the dreaming state and you recognize the signal and become lucid.
Dr. LaBerge invented this technique while doing work for his doctorate. He has been perfecting the technique since then and released one device for it: The Nova Dreamer. There are more devices out there, but it is the most famous.
Externally Induced Lucid Dream Tutorial