A feature of automatic call distributors (ACDs) that enables an impatient caller to register the desire to be called back by a call center agent, rather than wait in a seemingly interminable queue.When the queue has been satisfied and an agent becomes available, the system will call the customer back and connect him to an agent automatically, perhaps using a predictive dialer in a call blending application. See also ACD, call blending, call center, and predictive dialer.