So, I’ve stumbled on a big rumbling discussion, largely sparked by MJ Young’s Article at Places to Go, People to Be.
The discussion was picked up in several places: On the 20×20 room (which sparked a response, here) and on the Master’s Council.
Here are some direct links to definitions: Illusionism, Participationism, Trailblazing, and Bass playing (um, not so linked). Others include No Myth, and Background Based Gaming. Unfairly overlooked: Pinball or Open Sim, which doesn’t have a really good link.