A standard electronic flight ticket (e-ticket) number is a unique 13-digit identifier that serves as your official contract of carriage. It is distinct from the 6-character alphanumeric PNR (Passenger Name Record) or "Booking Reference." The 13-digit string is structured specifically: the first three digits represent the IATA numeric code of the issuing airline (e.g., 001 for American Airlines, 016 for United, or 125 for British Airways). These are followed by a 10-digit serial number unique to your specific purchase. You can find this number on your confirmation email, usually labeled as "Ticket Number" or "ETKT," or at the bottom of your boarding pass. Knowing this number is crucial for claiming frequent flyer miles, requesting refunds, or checking in for international flights when the reservation system cannot find your PNR. It acts as the actual proof of payment, whereas the PNR is simply a link to your itinerary in the airline's computer system.