"Airline" is the airline you used for this flight.
There are three ways to find airlines:
Enter the airline name or a part of it (e.g. "Cathay Pacific", "Cathay", "Cath") or the airline code (IATA "CX", ICAO "CPA") and wait for a second. A list of matching airlines will appear in the drop-down box. Alternatively, if you're sure you know the code, just immediately hit TAB or ENTER, and then OpenFlights will match it for you.
Enter a flight number like "CX123" into the Flight # box, and OpenFlights will automatically match "CX" to Cathay Pacific and fill in the airline for you.
Click on to pop up a search dialog, where you can find the airline by name, country name or airline code, and even enter new airlines if they're missing from the database.