I’m not sure there is, at least as we understand it. Not at the moment, anyway.
When we speak of “casual” we mean a cluster of things. Sometimes we mean targeting a different demographic, one not excited by the hardcore fantasy-and-sci-fi fictions we concoct. Sometimes we mean shorter play sessions. Sometimes we mean things like not requiring grouping in the worlds, which makes it easier for a less dedicated player to have fun.
More “casual” experiences often have a connotation of being shallow. One thing that is clear, though, is that it doesn’t matter how casual you make an experience, some people will use it in a hardcore manner. And that means that it must have hidden depths of some sort. A shallow experience simply doesn’t tend to keep people.
