Final answer:
The National Bureau of Economic Research (NBER) is the organization that defines business cycle peaks and troughs in the United States.
Step-by-step explanation:
The name of the organization that defines business cycle peaks and troughs in the United States is the National Bureau of Economic Research (NBER). It is a private think tank that tracks business cycles for the U.S. economy. The NBER determines the official ending dates of recessions and the beginning dates of recoveries.