What Is Callsign? Definition & Meaning in Aviation
A callsign is the identifier a flight uses on the radio and in air traffic systems, usually the airline’s three-letter ICAO code followed by the flight number.
In plain language
It often differs from the flight number printed on the ticket. For example, a flight sold as PK 300 may appear on the radar with the callsign PIA300.
Example
On this site, flights are matched by callsign, which is why you can search either PK 300 or PIA300.
Why it matters
The callsign is the key to finding a flight on a tracker. If a search by flight number returns nothing, the callsign may differ, or the operating airline may be a different one from the airline you booked.