Plain English Meaning
Equipment installed at an airport that fixes small errors in GPS signals and sends the corrections to nearby aircraft, so they can fly very precise approaches to the runway using GPS instead of a traditional ILS.
Full Definition
A ground-based system that improves the accuracy, integrity, and availability of GPS signals within the local area of an airport, enabling precision approach and landing guidance comparable to or better than an Instrument Landing System (ILS). A GBAS ground station receives signals from GPS satellites, calculates correction , and broadcasts that data via a to suitably equipped aircraft on .