The Big D, and I don't mean Dallas

a 10% decline in the markets is called a correction.
a 20% decline in the markets is called a recession.

what is a 50% decline in the markets called?

Oct 2007, Dow Jones Industrial Avg: 14,121
Feb 2009, Dow Jones Industrial Avg: 7,062

http://finance.yahoo.com/q/bc?s=^DJI&t=my&l=off&z=m&q=l&c=