The term "wait list" is not a DanceCloud term - it's been used by dance organisers for a long time. It describes a list of dancers who want to book for an event, but cannot be sold tickets immediately. The list is maintained so that as places become available at the event, people on the wait list can be notified and asked to complete their booking. Wait lists are widely used by dance organisers, so DanceCloud is built to help them manage the process.
When you register for an event on DanceCloud, we check whether you can be sold your desired ticket(s) straight away. You may not be able to if there are too many of one role (lead/follow) booked for the event, or if the event is currently sold out. If either are the case, you can choose to join the wait list and DanceCloud will notify you when spaces become available.