An Aircraft Report is a report of actual weather conditions encountered by an aircraft while in flight. There are two types of reports. An AIREP is a routine, often automated report of in-flight weather conditions such as wind and temperature. A PIREP is reported by a pilot to indicate encounters of hazardous weather such as icing or turbulence. Both are transmitted in real-time via radio to a ground station.
PIREPs and AIREPs are encoded differently. AIREP format is more common outside the contiguous U.S. even though there are some AIREPs over the CONUS. The location is specified by latitude and longitude which is better for international routes. PIREPs are preferred over the CONUS where the location is based on distance and direction to a known Nav Aid such as a VOR.