system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How is it possible that, if I search for a Home Theater at any website, the entire god damn internet is going to start showing me Home Theater ads?
gpt
because you're being tracked by cookies and there are only a couple of notably ad delivery networks.  You search at google and they know you're interested in it, then you go to another site that monetizes it's content with ads that are delivered by google...so...google gives you an ad related to the thing you search for, and so on ,and so forth.