The National Bureau of Economic Research (NBER) has designated nine business cycles over the years from 1945 to 1991. During this period, the average business cycle lasted about five years; the average expansion had a duration of a little over four years, while the average recession lasted just under one year.
A recession is a significant decline in activity spread across the economy, which lasts more than a few months and is visible in industrial production, employment, real income, and wholesale-retail sales. A recession begins just after the economy reaches a peak of activity and ends as the economy reaches its trough. Between trough and peak, the economy is in an expansion. The expansion is the normal state of the economy; most recessions are brief, and they have been rare in recent decades.