Also referred to as a short code, or six digit phone number, six-digit codes are numbers created by major wireless carriers. These phone numbers allow marketers to communicate with consumers about things like promotional offers, new products and services.

In the context of travel and aviation, a 6-digit (or 6-character) alphanumeric code is almost always your PNR (Passenger Name Record), also known as a Booking Reference or Record Locator. This unique code is the "key" to your entire travel itinerary. When you book a flight, the airline's Computer Reservations System (CRS) generates this 6-character string (e.g., J4K2L9) to identify your specific file, which contains your name, flight details, ticket number, meal preferences, and contact information. You need this 6-digit number to check in online, manage your booking, or make changes to your flight. It is fundamentally different from your 13-digit ticket number, which represents the "payment" for your seat, whereas the PNR represents the "reservation" itself. It is crucial to keep this number private; anyone who has your 6-digit code and your last name can potentially access your personal data or even cancel your flight. In 2026, this 6-character code remains the industry standard for identifying individual travelers across the global distribution systems (GDS) used by airlines and travel agencies worldwide.