Plain English Meaning
It is a weather add-on built into the airport's main surveillance radar. The radar already tracks aircraft, and this add-on uses the same returns to spot dangerous wind shifts and microbursts near the airport so controllers can warn pilots.
Full Definition
A weather-detection enhancement added to the FAA's ASR-9 airport surveillance radar that processes radar returns to detect wind shear, microbursts, gust fronts, and precipitation in the airport terminal area. When hazardous conditions are identified, alerts are passed to air traffic controllers, who relay them to pilots arriving at or departing from the airport.