Or perhaps better stated by the author of the tool, A Simple Standards-Based Semantic Slide Show System or S⁵. In Eric’s own words:

With one file, you can run a complete slide show and have a printer-friendly version as well. The markup used for the slides is very simple, highly semantic, and completely accessible… It’s totally simple, and it’s totally standards-driven.

You really should at least check out the demo to understand how cool this is.