Remarketing is targeting your ad campaigns to users who have previously visited your website.
Ads are shown to users who have already visited the company’s site. You do not have to come back here to see the ads – they can be displayed on all resources where the Google Adsense program works. A company need only place remarketing code on all pages of their site. A cookie is written directly to the device used by the resource visitor, recording that its owner has been to the company’s site. This allows the advertiser to use the very mechanism of re-marketing to the user.