Direct response marketing is a form of marketing designed to solicit a direct-response, which is specific and quantifiable. The delivery of the response is direct between the viewer and the advertiser, that is, the customer responds to the marketer directly. This is in contrast to direct marketing in which the marketer contacts the potential customer directly.
In direct marketing (such as telemarketing), there is no intermediary broadcast media involved (which is why it is called direct). In direct response marketing, marketers use broadcast media to get customers to contact them directly. It is direct response marketing because the communications from the customer to the marketer is direct, and this differentiates it from direct marketing in which the communications from the marketer to the customer is direct.
Like direct marketing, direct response seeks to elicit action. It is inherently accountable since results can be tracked and measured. Furthermore, direct response campaigns perform best if the underlying strategies and tactics are highly competitive... - Wikipedia