In addition to creating Registrants, you can also add Guests. Guest records have many of the same fields as Registrants, but as they can’t exist in Raiser’s Edge without a link to a Registrant. Guests rely on the fact that there is already a participant mapped to act as host.
Guests are looked up in one of two ways. If a constituent id is mapped, then the guest will be created from that constituent and added to the event. Otherwise the application will look to see if there is a non-constituent participant with the same first and last name in the event. If it cannot find this participant, then it will create a new non-constituent participant and make it the guest of the mapped participant.

Above, you can see a sample Guest mapping (note that the Constituent ID is shown as ID).