A United Airlines Travel Certificate is a form of credit issued to passengers for various reasons, such as flight cancellations, service disruptions, or as part of a promotional offer. It can be used to pay for future flights with United Airlines. The certificate typically has an expiration date, often one year from the issue date, and is non-transferable, meaning it can only be used by the individual to whom it was issued. To redeem it, you can apply the certificate code during the payment process when booking a flight on United\'s website or app.