Google Analytics is one of many web analytics tools or services that allow you to track website traffic, performance and behaviour. The basic version of Google Analytics is free to use, but there is a premium version available, which costs upwards of $150,000 per year.
By implementing the tracking code provided by Google onto all your site’s webpages, you can track a huge range of metrics and data about the people who visit your site. This is anonymised data, so you cannot determine who did something, just that X number of people did something.
This type of service is invaluable for website owners, SEOs, Digital Marketers, online businesses, etc. Using Google Analytics, you can see how many people visited your site in any given date range, what pages were visited, if they added a product to a basket or made a purchase. These are just some of the things you can track, measure and report on using the data provided by Google Analytics.
There are alternatives to Google Analytics such as Omniture or Adobe, but Google Analytics is by far the most popular and ubiquitously used of all web analytics services.