Google Analytics is a feature which allows “webmasters”, designers/developers to monitor site traffic. Google Analytics breaks down your traffic into 3 categories:

* Direct Traffic: these are the people who typed in your URL into the address bar, bookmarked your site earlier, or followed a link from an email.
* Referral Traffic: this traffic arrives when someone is at another Web site and clicks on a link to your site.
* Search Engine Traffic: these people found you via a search at Google, Yahoo or another search engine.

In addition, you can also see which search terms people used to find your site under the Keywords tab.

Very very useful, and easy to install and use! More information available from here.