Remarketing (or retargeting) is the strategy of showing personalized ads to people who visited your site, added products to their cart, partially completed a form, or interacted with your content. It is one of the most effective advertising tactics, with conversion rates 3-5x higher than cold traffic.
A visitor viewed 3 pairs of shoes on your site but did not buy. Through dynamic remarketing, you show them those exact 3 pairs with the message 'Still thinking about it? Free shipping today!' — conversion rate is 8%, vs 2% for new traffic.