This document defines key terms related to business cycles and fluctuations such as recessions, peaks, troughs, expansions, and leading economic indicators. It describes the typical phases of a business cycle as consisting of recession, trough, expansion and peak. It also discusses some common causes of business cycles, including changes in investment and innovation, monetary policy decisions, and external shocks. The document notes that leading economic indicators and composite indexes can be used to forecast changes in GDP and the timing of recessions and recoveries.