General declaration
The general declaration, or gen dec, is the standard ICAO customs document that lists an international flight's aircraft, crew, passengers, route and any declarations, and is presented to customs and immigration on arrival and sometimes departure. The crew or handling agent prepares it from the passenger details you provide; that is why operators ask for full names, dates of birth, nationalities and passport numbers well before the flight. Errors on the gen dec, such as a mis-spelt name or expired passport, can delay clearance or lead to refusal of entry, so send exactly what is printed in the passport rather than a nickname or a shortened name.