Plain English Meaning
At some airports, the runway lights are not left on all the time. The pilot turns them on by clicking the microphone button several times on a specific radio frequency. More clicks make the lights brighter.
Full Definition
A system at certain airports that allows the pilot to activate and adjust the intensity of runway and approach lighting from the cockpit by keying the aircraft's radio microphone a specified number of times on a designated frequency, typically the airport's CTAF or UNICOM.