Definition of source key

code used for the statistical reporting and tracking of direct- marketing response that combines source information with data pertaining to campaign, list, package, offer, and so forth. The source key is printed on reply forms and is entered into a computer along with the order information. Order and customer volumes and other statistics are then tracked and tabulated by source key. Source keys vary in size, but most are four to six digits long. Although they provide essential information, marketers prefer to keep source keys as short as possible, in the belief that long code numbers on a reply form discourage response.