It is the two-letter code that is used to identify Southwest Airlines flights on schedules and in flight information. The code WN was assigned to Southwest Airlines by the International Air Transport Association.

In the aviation industry, "WN" is the two-character airline designator code for Southwest Airlines. These codes are assigned by the International Air Transport Association (IATA) to identify airlines for ticketing, boarding passes, flight schedules, and baggage handling. While many codes are intuitive (like AA for American Airlines or DL for Delta), others are less obvious. The "WN" code was actually inherited; when Southwest was starting out, more logical codes like "SW" were already taken by other carriers (in that case, Seaboard World Airlines). Southwest chose "WN" and has used it ever since. You will see this code on airport flight monitors (e.g., WN 1234) and on your boarding documents. Interestingly, the airline's three-letter ICAO code—used by air traffic control—is "SWA," but for the general traveling public, "WN" remains the primary identifier for the world's largest low-cost carrier.