the root of such words as spiffy and spiiferific (although the latter is a compound word including terrific). Used mainly as an expletive in much the same was as fuck although can be used as a remark of amazement, shock or suprise.
Boss: "You are going to have to work overtime."
Worker: "Spiff!"
Grocery Clerk: "You just won the sweepstakes."
Shopper: "Spiff!"