Most people that visit your website won't convert on the first visit. Retargeting is a way to bring back potential customers and convince them to convert.
You might have experienced this yourself after checking out a product online. It seems like ads for that product appear on every site you visit afterward.
This type of marketing has been proven to be very effective at converting lost customers. You often have the option to use either generic retargeting ads (maybe brand-level information or best-selling products) or dynamic retargeting ads (products that either the customer viewed or are related to those they viewed).
Retargeting is not to be confused with remarketing. Retargeting uses paid ads to target people who visited your site but didn’t convert. Remarketing is typically done through email and targets previous customers.