CPCcost per clickadvertising is the most common way to make money by accepting ads on your site. With CPC, an advertiser pays a fee when someone clicks its link on your site, and you get a portion of that fee. CPC ads are mostly (although they don't have to be) text-only.
The idea of making ads contextualthat is, relevant to the content of the web page near the adis closely bound up with CPC advertising. CPC ads that are contextual are much more effective, and generate more revenue for a site owner, than ads that are not contextual. But, it is worth bearing in mind that you can have CPC ads that are not contextual, and, conversely, contextual ads that pay on some other basis than CPC.