Cancellation Reason Codes are only used by your association staff who have access to the Adjustment Wizard. If a meeting registration needs to be cancelled, staff can select a reason for the cancellation from a drop down menu.
The Cancellation Reason Codes Dictionary is a flat table where these reasons for cancelling a registration are defined. Sample MasterCodes for the GroupType Cancellation Reason Codes (CANCELED) are seen in the next screen shot. 
Those seen above are typical examples, but you can add as many as you need to customize the choices available in the Adjustment Wizard. More information on the Adjustment Wizard is in its section of this knowledge base.