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There are two definitions of a recession.

The first, the simplest one, is two consecutive quarters of economic decline. Two calendar quarters where the economy produced less than the quarter before.

The second definition looks at a decline in general economic activity. So that takes into account not just GDP but also employment, retail sales, a whole host of different indicators, and uses that to make a call about whether there's a recession or not.

The nice thing about that definition is that because it's more broad-based, you get a better idea of what's happening with the economy. The downside is that because it's more subjective, it's a bit like how the U.S. Supreme Court defined pornography: It's a recession if it looks like a recession.