Plain English Meaning
A system of equipment installed at an airport that fixes small errors in GPS signals and broadcasts the corrections to aircraft nearby, so they can fly very accurate GPS-based approaches to that airport.
Full Definition
A ground-based augmentation to GPS that improves the accuracy, integrity, and availability of GPS signals within the local area surrounding an airport, enabling precision instrument approaches down to and including Category I, II, and III minimums. A LAAS installation consists of GPS reference receivers at known surveyed positions on the airport, a central processing facility, and a VHF data broadcast that sends and integrity to suitably equipped aircraft. LAAS has since been formally renamed the (GBAS) by the and .