Whenever you make an airline reservation, you get something called a PNR—a six-letter or six-letter and digit confirmation code. But you also receive something more important: a 13-digit electronic ticket number. 

This number is crucial. The first three digits designate the airline (e.g., 001 is American, 006 is Delta, and 027 is Alaska), and the remaining 10 digits are your individual ticket number. 

Confirmation codes can change, but ticket numbers don’t. If you lose your ticket or need to make changes, that 13-digit number is your go-to.