Have you noticed familiar advertising that seems to be popping up everywhere after you have visited a website?
There is a concept called retargeting and remarketing, coined somewhat by Google, that basically tracks the sites you visit and then delivers advertisements related to those sites on subsequent sites that you visit in the future. This is a way of reinforcing a brand.
Experts say that it takes up to 8 exposures to a brand before it becomes recognizable. So, if you happen to land on a website featuring a brand or a product, Google takes note of it. If that brand is a Google display advertiser then the next website you visit that features Google display advertising, it is quite likely that Google will deliver an ad from that website you visited earlier. After a while, the brand becomes noticeable and highly recognizable. The likelihood that you will click on that ad (conversion) is significantly higher after those multiple exposures.