Tracking & Analytics
For website owners who want to track traffic to and on their site, search engines such as Google and Bing provide certain programs to enable the owner to do just that. Google Analytics, Google Webmaster Tools, and Bing Webmaster Tools all use visual data and activity reporting to give the site owners useful data so as to inform them on how to develop or improve their website.
Google Analytics is a website traffic analytics tool which allows site owners to track and analyze traffic and user behavior on their website. This is an essential part of understanding a site in relation to SEO, by finding out what is working and what is not.
Google Analytics (and other similar analytics tools) provide highly detailed information which includes number of visitors, what people are doing on the site (e.g., the pages which they visit, how long they stay on the site, how they get to the site, etc.), giving webmasters the understanding and insight they need to make effective decisions about how to improve their site, both for users and search engines. More information can be found on the Intro to Google Analytics Help Page.
Google Webmaster Tools
The Google Webmaster Tools provides site owners and marketing agencies with valuable and actionable information to help improve the functionality of websites and at the same time improve the chances of having improved organic search engine rankings. According to Google, the purpose of the Webmaster Tool is to "help provide the data, tools, and diagnostics for a healthy, Google-friendly site."
Bing Webmaster Tools
Bing Webmaster tools provides almost identical functionality as does Google Webmaster Tools.