Retargeting is the practice of serving ads based on prior engagement. While there is more than one form of this technology, the most frequently used is site-based retargeting. (Other forms include search retargeting, email retargeting, facebook retargeting, and CRM retargeting.)

Site-based retargeting is the practice of serving ads to people who visit your website after they leave. These ads appear on a variety of other sites around the web, keeping your brand in front of your bounced site visitors in an attempt to bring them back.