Google Analytics is a free service offered by Google that generates detailed website visitor statistics. It is used by 55.8% of all websites and has an 81.5% market share. The Google Analytics Tracking Code is a piece of JavaScript code that is added to every page of a website to track visitor behavior. Google Analytics allows users to measure metrics like total traffic, page views, visitor locations, and goals/conversions in reports that can be filtered by date ranges and dimensions.