What the hell is a rubric cube?

I think that the easiest way to answer this question is to start by looking at exactly what a rubric is. According to Google there are many many definitions of the word rubric. Most are to do with education. My favourite would have to be:

[A rubric is...] a heading, title of a printed matter, where the data is organized and united under one commonly related theme

In reality I chose the name because rubik's cube was taken, and this sounds much more clever than that!