From Boyes and Melvin, Macroeconomics, 8th edition, 2008, pg. 135:
>The official dating of recessions in the United States is the responsibility of the National Bureau of Economic Research (NBER), an independent research organization. The NBER has identified the shaded areas in the graph in Figure 1 as
recessions and the unshaded areas as expansions. Recessions are periods between
cyclical peaks and the troughs that follow them. Expansions are periods between
cyclical troughs and the peaks that follow them.
>The NBER defines a recession as “a period of significant decline in total
output, income, employment, and trade, usually lasting from six months to a
year, and marked by widespread contractions in many sectors of the economy.”
People sometimes say that a recession is defined by two consecutive quarters of
declining real GDP. This informal idea of what constitutes a recession seems to
be consistent with the past recessions experienced by the United States, as every
recession through the 1990s has had at least two quarters of falling real GDP.
However, this is not the official definition of a recession. The business cycle dating committee of the NBER generally focuses on monthly data. Close attention
is paid to the following monthly data series: employment, real personal income
less transfer payments, the volume of sales of the manufacturing and wholesale–
retail sectors adjusted for price changes, and industrial production. The focus is
not on real GDP, because it is measured only quarterly and does not permit the
identification of the month in which business-cycle turning points occur.
>The official dating of recessions in the United States is the responsibility of the National Bureau of Economic Research (NBER), an independent research organization. The NBER has identified the shaded areas in the graph in Figure 1 as recessions and the unshaded areas as expansions. Recessions are periods between cyclical peaks and the troughs that follow them. Expansions are periods between cyclical troughs and the peaks that follow them.
>The NBER defines a recession as “a period of significant decline in total output, income, employment, and trade, usually lasting from six months to a year, and marked by widespread contractions in many sectors of the economy.” People sometimes say that a recession is defined by two consecutive quarters of declining real GDP. This informal idea of what constitutes a recession seems to be consistent with the past recessions experienced by the United States, as every recession through the 1990s has had at least two quarters of falling real GDP. However, this is not the official definition of a recession. The business cycle dating committee of the NBER generally focuses on monthly data. Close attention is paid to the following monthly data series: employment, real personal income less transfer payments, the volume of sales of the manufacturing and wholesale– retail sectors adjusted for price changes, and industrial production. The focus is not on real GDP, because it is measured only quarterly and does not permit the identification of the month in which business-cycle turning points occur.