Definition
A satellite-based augmentation system that improves the accuracy, integrity, and availability of GPS signals over a wide geographic area. WAAS uses a network of ground reference stations to monitor GPS satellite signals, calculate correction data, and broadcast those corrections through geostationary satellites to suitably equipped aircraft receivers. The corrections allow GPS to be used as a primary means of navigation for all phases of flight, including precision-like approaches with vertical guidance.
Plain English
A system that fixes small errors in regular GPS signals so the position shown in the cockpit is much more accurate. It does this by checking GPS from ground stations and sending the corrections to the aircraft through extra satellites.
Context Anchor
You will see WAAS in GPS navigator information, aircraft equipment descriptions, and GPS instrument approach procedures.
Derivation
Wide Area refers to the broad geographic coverage (most of North America). Augmentation means adding to or improving something — here, improving plain GPS. So the name simply describes what it does: it augments GPS signals across a wide area.
Why Pilots Care
It enables precision approaches with lower decision altitudes using GPS alone, increasing access to airports without ground-based aids.
Analogy
Think of WAAS as a checking system for GPS. GPS gives the aircraft its position, and WAAS helps correct that position and confirm that it is safe to use.
Intuition Check
Do not think of WAAS as a separate navigation system replacing GPS. WAAS improves and checks GPS information so the aircraft GPS can use it with more confidence.
Example Sentence 1
The pilot confirmed the GPS was receiving WAAS signals before selecting the LPV approach.
Example Sentence 2
WAAS allows the aircraft to fly a precise path to the runway using satellite corrections.