Inflection Point—(noun) a point on a curve at which the curvature changes from convex to concave (A.K.A. When things go from good to bad—instantly).
Example: Saturday, October 17th, 2009: the most critical day in Kansas Football history.
From the fall of 2007 to October 17th, 2009, the Kansas Jayhawks were 25-6, they had won a co-Big 12 North Championship, an Orange Bowl, an Insight Bowl, were 5-0 on the young season, ranked No. 17 in the country, and had a perennial Heisman trophy candidate, Todd Reesing, leading the charge. But from October 17th to date, Kansas has gone 5-21, has lost to the North Dakota State Bison, lost the last 5 meetings with their rivals, Missouri and Kansas State, and has returned to their place as Big 12 doormat.