This is the name of the directory where compiled templates are located. By default this is ./templates_c, meaning that Smarty will look for the templates_c/ directory in the same directory as the executing php script. This directory must be writeable by the web server, see install for more info.
Technical Note: This setting must be either a relative or absolute path. include_path is not used for writing files.
Technical Note: It is not recommended to put this directory under the web server document root.
See also $compile_id and $use_sub_dirs.