Google Analytics is simply a service provided by Google (free of charge) to track the performance of your website. Most Google Analytics tracks visitors on your site – how they got there, what they do on your site, the amount of time they spend, and a host of information. It’s highly customize able meaning the possibilities are endless as far as the type of information/reports it can generate.
For a more complete explanation on Google Analytics you can also take a look at the “what is Google Analytics” topic over on Google’s own site.
Link: InspiredMag