Content Templates - allow you to save preformatted blocks of content, so you can apply template for repeated use, such as in creating or editing wiki pages.
Smarty Templates - commonly known as .tpl files - are the presentation files that work in conjunction with .php files to produce the site pages.
A Tiki theme (or visual skin, also called a template in some other Web contexts) can have its own custom variants of template (.tpl) files for specific parts of the page or features, although this isn't recommended, due to the problem of keeping them in sync as the default files evolve in new Tiki releases.