Plain English Meaning
The radios and instruments in the cockpit that help the pilot figure out where the aircraft is, where it's going, and let the pilot talk to controllers and other aircraft.
Full Definition
The collective set of onboard avionics that allow a pilot to determine the aircraft's position and intended course (navigation) and to exchange voice or data messages with air traffic control and other stations (communication). Typical components include VHF communication radios, VOR and ILS receivers, GPS units, transponders, and audio panels.