The document discusses the business cycle, which refers to the regular fluctuations in economic activity between periods of expansion and contraction. It describes the different types of business cycles including minor, major, very long period, and Kuznets cycles. The phases of the business cycle are also outlined, including expansion, peak, recession, and trough. Finally, the document analyzes various internal and external causes that can trigger business cycles such as consumer spending, investment, government policy, technology, and human psychology.