What is a depression and are we in one?

DQ here.  In a comment to another post, Charles Martel says we are in a “depression economy” and that Obama is prolonging the depression.  I’d be interested to know how Bookwormroom readers define “depression” (and “recession” for that matter) and whether they agree we are in one.  Also, if we are in one, how does an economy get out of a depression/recession and what, if anything, is Obama doing to prolong whatever it is we are in now?