It's Sony's re-release of a movie with a higher bit-rate sampling and usually a re-mixed dts soundtrack.
Sony's superbit explanation page
They say that movies are picked based upon whether or not they will benefit from the process, mainly action movies. Not all superbits are neccesarily good movies, just high action.
I think it's similar to other studio's stuff, like the Criterion Collection, or New Line Platinum series.
