Self-Modifying Artificial Intelligence is a term made by politicians, the news media, or angry mobs for more or less unrestricted Artificial Intelligent beings. It clearly wasn't an artificial intelligence researcher, because they all do that.
That said, a S.M.A.I. does have more free reign on the self-modifying part. Specifically, they're more able to think outside the box, and they can formulate their own objectives, unlike more limited AIs who merely seek the goals that they have been programmed to seek.