A superlative of the highest order and magnitute.
It has its root in the word Superb.
The word was first said by Shang Tsung in Mortal Kombat on the N64. The character was supposed to cry "Superb!" in response to a particularly tasty uppercut, but due to a freak alginment of the planets and a mystical symbol drawn in the dust of the N64 console, he actually uttered the cry "UMPERB!".
Others theorise that the anomaly was created through poor rendering provided by the N64's sound chip, but no-one can be sure.
"That's a superb pie"
"It's better than superb - it's umperb!"