Ever seen an ad on Facebook or around the web and then happen to see that SAME ad the next day, the next day and maybe the next day? You've been Remarketed or Retargeted. And it's 100% ethical and legal. You've probably clicked on an ad because you were interested in the product but maybe you didn't buy. The advertiser has a piece of "code" on their website that communicates with the advertising platform (in the background) that someone clicked their ad. That's why you see the ad over and over until you ask NOT to see it.
Remarketing (or Retargeting) is the action of re-marketing or re-engaging your visitors and customers with highly targeted ads based on their recent interaction with your product or service when they leave your website without buying from you.
Facebook Remarketing would then consist of retargeting those visitors and potential customers who have shown some interest in your product or service by using the Facebook Advertising Platform.
It’s a fact that some people buy in the first visit, but we are talking about 1% to 2% of them. What about the other 98%? Yeah, squeeze pages can grab some leads, so you may target around 30% to 40% of those people by email marketing, but you are still wasting more than half of your visitors.
Another really cool fact is that a lot more people buy after having several contacts with your offer, so it just makes good sense to use remarketing as part of your business model.