External references are a unique string of characters (not limited to numbers) that are populated by an event organiser when profiles are imported. These are used to identify profiles in the Core and may include Staff ID, registration number, ticket number etc.
External references can be very useful when importing profile lists. Using external references when uploading profile data minimises the risk of duplicating your profile list by mistake, as this number can be used to separate those existing profiles from ones yet to be created. This is also important when bringing attendee data from a third-party system with pre-existing registration or ticket numbers, as to keep the data clean and trackable.
While a primary function of an external reference is as profile identification, it can also be used to log into the event App. It is particularly useful to use an external reference as a login method when the reference is something the attendee is already familiar with (e.g. staff ID or member number), as this limits confusion and required attendee communication.