At shadowstats.org you can find Hyperinflation Special Report from 8 April 2008.
From that report, a definition of Hyperinflation:
Hyperinflation: Extreme inflation, minimally in excess of four-digit annual percent change, where the involved currency becomes worthless. A fairly crude definition of hyperinflation is a circumstance, where, due to extremely rapid price increases, the largest pre-hyperinflation bank note ($100 bill in the United States) becomes worth more as functional toilet paper/tissue than as currency.
more to come . . .