Plain English Meaning

Each aircraft figures out where it is using GPS, then continuously broadcasts that information by radio. Ground controllers and nearby aircraft pick up the signal and can see exactly where everyone is.

Full Definition

A surveillance system in which an aircraft automatically determines its own position using onboard navigation sources (typically GPS) and broadcasts that position, along with identification, altitude, velocity, and other data, on a defined radio frequency. Ground stations and other suitably equipped aircraft receive the broadcast and use it for traffic surveillance, separation, and situational awareness. ADS-B Out refers to the aircraft transmitting its data; refers to the aircraft receiving and related services such as traffic and information.