Plain English Meaning
A device circling the Earth that sends signals down to aircraft. Receivers on the plane use those signals to work out where the aircraft is and what time it is, accurately enough for navigation.
Full Definition
An object placed in orbit around the Earth that transmits signals used for navigation, communication, or weather observation. In aviation, satellites form the space segment of Global Navigation Satellite Systems (GNSS) such as GPS, broadcasting precise timing and position data that aircraft receivers use to determine location, altitude, and time.
Context Anchor
Seen in discussions of GPS, navigation, and that use signals from space.