The AdSense Overview

Google AdSense is an extension of Google AdWords. Specifically, the AdSense
program allows non-Google Web sites to display Google advertising (AdWords
ads), and then share the revenue Google charges advertisers when site visitors
click through the displayed ads. Clear as mud? Well, look at it this way:
Google ads appear not just on Google but on thousands of sites all over the
Web. These sites serve as syndicators of Google ads. (See Figure 11-1.)
196 Part III: Creating Site Revenue with AdSense
So, what does this seemingly slapdash distribution of Google ads do to the
vaunted relevancy of AdWords and search advertising? On Google, AdWords
ads are associated with keywords and are displayed when somebody searches
on those keywords. When the advertiser does a good job choosing keywords
related to the advertised site or product, relevancy is automatic and chances
are good that the ad is of interest to the Google user. What kind of relevancy
ensues when AdWords ads are displayed on a non-Google site — a site that is,
in most cases, not even a search engine?
Google builds relevancy between ads and their host sites by analyzing the
sites and determining keywords appropriate to them. This task might seem
presumptuous, but remember how much experience and success Google has
in crawling, absorbing, understanding, and indexing Web pages. After all,
Google is in the keyword-matching business and is arguably better at making
those matches than any other company in the world. So if you trust Google to
find Web pages matched to keywords, there’s no problem trusting Google to
display relevant ads on AdSense sites. It’s all about keywords.