[Larrikin]

If you're browsing a computer tech website you get shown ads for GPUs and other tech items. If you're browsing an article on remedies for dealing with cramps you get shown ads for feminine hygiene products.

Maybe on both sites you get shown ads for coca cola or a car.

None of those require building up a profile that tracks your personal browsing habits across the entire internet and is simply targeting your customers where they are.