I did some googling and "ultraintelligent machine" seems to derive from a 1965 I.J. Good article.
My feeling is that such a tag would largely refer to his work, and that superintelligence more current term, possibly favored for its compactness.
- Wiki search for superintelligence leads to a page of that title
- Wiki search for ultraintelligent machine leads to I.J. Good page
Let an ultraintelligent machine be defined as a machine that can far surpass all the intellectual activities of any man however clever.
Good's definition ultraintelligent machine:
My thinking is we need both, because Good is quite important, and ultra intelligent machine should refer largely to his work.
By contrast, superintelligence should be used to refer to the concept in general.
- From a practical standpoint, I suspect superintelligence is more widely used, and likely sought for as a tag. One who doesn't know Good's work might not think to search for ultraintelligent machine.