To illustrate: One can have many templates that can be choosen from in the admin the base template directory/folder structure would look some thing like this where each folder would be a different template
they would be in alpha order)
Code:
/templates
/classic
/template_default
/spring
/summer
/fall
/winter
/red
/any_other
and in side each one of these there would be a template_info.php file edited to correspond to the template name, a css folder with the css for this template and so forth. All things pertinent to this template that are at this root folder level.