Plain English Meaning
A heads-up from ATC, based on what they see on radar, telling you about another aircraft near you so you can look for it and stay clear.
Full Definition
Information issued by air traffic control (ATC) to alert a pilot to other known or observed air traffic that may be near enough to their position or intended route to warrant attention. The advisory typically includes the position of the other aircraft relative to yours (clock position), distance, direction of flight, and altitude when known.
Context Anchor
You may hear Radar Traffic Advisories from a while receiving , especially during , , , or .