What is a recession?

 NPR - A recession refers to a period of decline in economic activity. It's one of the four stages of the economic cycle: growth, peak, contraction (or recession) and trough.

Some analysts use a rough rule of thumb to identify recessions: Two consecutive quarters of decline in a nation's gross domestic product (GDP) — the broadest measure of economic activity. 

But the National Bureau of Economic Research (NBER) — the nonpartisan, nonprofit research organization that has become the semi-official arbiter of recessions — uses a somewhat squishier definition. It calls a recession a "significant decline in economic activity that is spread across the economy and that lasts more than a few months."

The job of documenting the economic cycles, including recessions, does not fall to the federal government.

Instead, the NBER's Business Cycle Dating Committee — made up of top American economists — has been declaring the beginning and end of the cycles since its creation in 1978 (NBER itself is decades older).

There is no fixed rule about how long NBER takes to identify a recession after a decline has started. It says on its website that past determinations have taken anywhere from four to 21 months.