For the vast majority of travelers, there is no functional difference between a PNR and a booking reference number; they refer to the same 6-character alphanumeric code (e.g., Z7Y4X2). PNR stands for "Passenger Name Record" and is the technical term used within the airline's Global Distribution System (GDS) to store your travel data, including itinerary, meal preferences, and contact info. The Booking Reference or "Confirmation Code" is the customer-facing name for that same record. However, a small distinction can arise in codeshare flights: if you book a flight through United that is operated by Lufthansa, you may have one "master" booking reference for United and a separate "airline-specific" PNR for the Lufthansa segments. You will need the specific operating carrier's PNR to select seats or check in on their website. Generally, if you are asked for either, you are looking for that 6-digit code found in the top right corner of your confirmation email or e-ticket, which serves as the "key" to access your entire reservation in the airline's digital database.