A slew of weak economic data, increasing trade tensions and slowing GDP growth have flashed signs of an economic slowdown. No one can predict exactly when a recession will occur. If the U.S. economy is in a recession, how will we know? The National Bureau of Economic Research, a nonprofit research organization, defines a recession as the period between a peak and a trough of economic activity. The organization doesn’t give a set definition of economic activity, but looks to indicators like domestic production, employment and retail sales.