Plain English Meaning
SBAS is the general name for satellite-based systems that fix small errors in GPS signals and warn pilots if the signal becomes unreliable. WAAS is the U.S. version of SBAS; other countries run their own.
Full Definition
A category of GPS augmentation systems that use a network of ground reference stations and geostationary satellites to broadcast correction and integrity information to GPS receivers, improving accuracy, availability, and trustworthiness of position data for navigation. Different regions operate their own SBAS: WAAS in the , in Europe, MSAS in Japan, and GAGAN in India.