Here. In case you missed it when it was attached to an earlier post by SteveH. And to help you out even further, here is the opening paragraph with emphasis added.

Determination of the December 2007 Peak in Economic Activity

The Business Cycle Dating Committee of the National Bureau of Economic Research met by conference call on Friday, November 28. The committee maintains a chronology of the beginning and ending dates (months and quarters) of U.S. recessions. The committee determined that a peak in economic activity occurred in the U.S. economy in December 2007. The peak marks the end of the expansion that began in November 2001 and the beginning of a recession. The expansion lasted 73 months; the previous expansion of the 1990s lasted 120 months.

It's the definition you said was the one you accept. And this recession you are trying to pin on Obama and the 111th Congress? It's a continuation of the Bush recession of 2007. Just because Bush didn't acknowledge the recession until Dec. 2008, doesn't mean it started then.

Again, name any Bush or Republican economic policy that the Dems in 110th Congress reversed or stopped once they, in your words, took control.