Wikipedia defines http://en.wikipedia.org/wiki/Typography
The JA Purity template has a number of hand coded CSS styles in its typography, and none of the bonus styles are displayed in the Joomla demo platform.
They are listed in the ja_purity/css/template.css file under a commented section Bonus Typography Styles. This article covers the various standard topography elements and the "bonus" styles and how to use them. The following images were generated using Firefox 3.0 on a Joomla 1.5.11 platform using JA Purity 1.2 as it accompanied that version of Joomla. Sample code is provided that generated the "bonus styles".