AdSense Relevancy, How Google Determines this?

There are many Adsense publishers that viewing the ads. So I believe you also think same thing like me: How are they going to get the relevant ads?

When attempting to match ads with those pages Google considers:

Entire keyword list associated with an ad group.
You want to use well themed keyword adgroups to help ensure your ads are delivered properly. Including generic words like laptop can make it harder for Google to understand what your adgroup is trying to sell.
Using appropriate campaign negative keywords can also help further target your ads.
Adgroup creative are also used to help understand what ads to display.
Max PPC and click through rate also play into the order of the ads displayed.