A retargeting pixel is a tiny piece of undetectable code which tags an anonymous cookie onto every visitor that visits your site or tracking link. Then, when those visitors leave your site or link with an embedded pixel, you can retarget them at a later time with more personalized ads.
Let’s say for example that you work with an influencer to drive his/her audience and traffic to your Amazon product. Though their audience might be very relevant to your product, it is likely that a majority of those clicks will not lead to a sale.
An embedded retargeting pixel allows you to tag every single person that clicks through your tracking link, so that you can retarget them with more ads (via Facebook, Twitter, LinkedIn, etc) for the same listing, or any other listing that might be relevant to your audience.