The World Wide Web isn’t a linear experience like leafing through and reading a book. The Web enables you to jump around from place to place. But in most cases, you jump from one page-based site to another. HTML is the specification for page-oriented Web navigation. VRML is a 3D navigation specification, hammered out by Silicon Graphics, Intervista Software, and other organizations and individuals.
It enables the creation of 3D sites (not necessarily just chat rooms, though this is one example of its use). Many sites and FAQs are devoted to discussing and showing off the technology. The specification is also available online.