It is my understanding that GAP (Group Amenities Plus) is a tool for travel agents to be used to offer group sailings some additional amenities for their cruise.
Mary Lou Scanlon
NCL Pride of America April 24, 2010
NCL Epic February 12, 2011
RCCL Allure of the Seas - September 18, 2011
Celebrity Eclipse - February 11, 2012:
RCCL Navigator OTS - February 9, 2013
Mary Lou is correct. A TA gets gap points based on the number of cabins sold. The TA can use the gap points to offer the clients such things as champagne & strawberries, tour conductor ticket, wine & cheese party, on board credits, etc.
Actually GAP points very on cruises not by cabins sold. Each sailing has a certain amount of GAP points offered to the TA to be used for onboard amenities for the clients. Not all ships and sail dates have GAP points though. These are also different from the tour conductor credits which do go by cabins sold.