A direct response campaign is an online advertising campaign whereby the advertiser want a direct and immediate response from exposed consumers.
Theoretically, digital media are ideal channels for direct response campaigns as the response is easy and rapid by the way of clicks and easily tracked and measured.
Many forms of direct responses can be sought after in digital marketing context:
clicks (visits) to the advertiser’s site
clicks + conversions (order, lead, etc.)
ad engagement / interaction (can be sometimes seen as branding campaign)
When the goal of a direct response campaign is a conversion, it has to be taken into account that the initial ad is only a part of the conversion process which takes place on the advertiser’s website.
The most part of digital advertising campaigns are direct response campaign and most are paid according to performances:
traditional display campaigns with direct response goals
PPC search ads
Direct response campaigns are often "opposed" to branding campaigns.
Direct response campaign illustrated by Yahoo: