A document that permits the use of a timeshare reservation by a guest of the owner, some clubs charge extra for a guest certificate.
Not all clubs or resorts allow guests certificates, but if your club does, it can be a great feature to have. The guest certificate allows your guest to check-in without you there. If you are going to be present for check-in and are simply taking guests with you, you won’t need a guest certificate and sometimes can skip a fee in the process.