Plain English Meaning
A system in the aircraft that watches nearby traffic and warns the pilots if another aircraft is getting too close, sometimes telling them to climb or descend to avoid it.
Full Definition
An onboard electronic system that monitors the airspace around an aircraft for other transponder-equipped aircraft, alerts the crew to potential collision threats, and, in more capable versions, issues coordinated vertical maneuver instructions to resolve the conflict.
Context Anchor
Seen in cockpit equipment, simulator scenarios, and training discussions about avoiding midair collisions.
Derivation
The name is built from its function: Traffic alert (warning the crew about nearby aircraft) and Collision Avoidance System (the means of resolving the ). It came into use in the 1980s as technology became reliable enough to support it.