The business cycle, also known as the economic cycle or trade cycle, is the downward and upward movement of gross domestic product (GDP) around its long-term growth trend. The length of a business cycle is the period of time containing a single boom and contraction in sequence. These fluctuations typically involve shifts over time between periods of relatively rapid economic growth (expansions or booms) and periods of relative stagnation or decline (contractions or recessions).
Business cycles are usually measured by considering the growth rate of real gross domestic product. Despite the often-applied term cycles, these fluctuations in economic activity do not exhibit uniform or predictable periodicity. The common or popular usage boom-and-bust cycle refers to fluctuations in which the expansion is rapid and the contraction severe.
The current view of mainstream economics is that business cycles are essentially the summation of purely random shocks to the economy and thus are not, in fact, cycles, despite appearing to be so. However, certain heterodox schools propose alternative theories suggesting that cycles do in fact exist due to endogenous causes.