Retired Documentation: You are using the documentation for version 1.7.3 which was retired in 2013. Go here for the latest version documentation or check here for your available upgrades to ExpressionEngine 3.
Global Template Variables
ExpressionEngine has a number of Template Variables that are global in scope, meaning they can be used anywhere within your templates. These variables enable you to show dynamic information, create links, display system information, control access to areas of your site, and more.