Plain English Meaning

Radar cannot see everything. It can be blocked by terrain, weakened by heavy weather, and may not show aircraft that are too low, too far away, or too close together. Pilots and controllers both have to keep these blind spots in mind.

Full Definition

The inherent constraints on what air traffic control radar can detect, display, and resolve, including range limits, line-of-sight blockage by terrain or the curvature of the earth, beam width effects, weather attenuation, target resolution between closely spaced aircraft, and reduced or no coverage at low altitudes or in remote . These affect the and of provided to pilots.