Plain English Meaning
A nationwide system of weather radars that shows where rain, snow, and thunderstorms are, how strong they are, and which way they are moving. Pilots use the picture it produces to plan a route around bad weather.
Full Definition
A network of high-resolution Doppler weather radars operated by the National Weather Service that detects precipitation intensity, movement, and certain severe weather signatures across the United States. NEXRAD imagery is distributed to pilots through ATC displays, Flight Service briefings, and cockpit weather data services, and is used for strategic avoidance of rather than penetration of storms.