Adverts above

I've been noticing lately that the adverts above are for websites I've previously visited. Is this just coincidence or is there some freaky google ad thing that is following everywhere I go?

I've noticed this with other websites. If I'm on one website and then go to a completely unrelated website, on the second website I see adverts that are related to the subject matter of the first website. It's a freaky Google thing. It's not a coincidence because Google tailors their advertising to the content of websites.