Parkin and Bade's text Economics gives the following definition of the business cycle:在帕金和巴德的经济学教材中，对商业周期给出了以下定义： " The business cycle is the periodic but irregular up- and- down movements in economic activity, measured by fluctuations in real GDP and other macroeconomic variables." “商业周期是经济活动的周期性但不规则的上下波动，以实际 GDP和其他宏观经济变量的波动来衡量。” To put it simply, the business cycle is defined as the real fluctuations in economic activity and gross domestic product ( GDP) over a period of time. The fact that the economy experiences these ups- and- downs in activity should be no surprise. In fact, all modern industrial economies like that of the United States endure considerable swings in economic activity over time. 简单地说，商业周期是指经济活动和国内生产总值在一段时间内的实际波动。经济在活动中经历这些起起落落的事实不足为奇。事实上，所有像美国那样的现代工业经济体，随着时间的推移，经济活动都会出现相当大的波动。 The ups may be marked by indicators like high growth and low unemployment while the downs are generally defined by low or stagnant growth and high unemployment. Given its relationship to the phases of the business cycle, unemployment is but one of the various economic indicators used to measure economic activity. For most detailed information about how various economic indicators and their relationship to the business cycle, check out A Beginner's Guide to Economic Indicators. 高增长和低失业率等指标可能标志着经济复苏，而经济低迷通常由低增长或停滞增长以及高失业率来定义。鉴于失业与商业周期各阶段的关系，失业只是用来衡量经济活动的各种经济指标之一。有关各种经济指标及其与商业周期的关系的最详细信息，请参阅《经济指标入门指南》。 Parkin and Bade go on to explain that despite the name, the business cycle is not a regular, predictable, or repeating the cycle. Though its phases can be defined, its timing is random and, to a large degree, unpredictable. 帕金和巴德继续解释道，尽管名字中有周期二字，但商业周期并不是一个规律的、可预测的或重复的循环。虽然它的阶段可以被定义，但其时间是随机的，并且在很大程度上是不可预测的。 The Phases of the Business Cycle 商业周期的各个阶段 While no two business cycles are exactly the same, they can be identified as a sequence of four phases that were classified and studied in their most modern sense by American e· conomists Arthur Burns and Wesley Mitchell in their text " Measuring Business Cycles." The four primary phases of the business cycle include: 虽然没有两个商业周期是完全相同的，而根据美国经济学家阿瑟·伯恩斯和卫斯理·米切尔在他们的著作《衡量商业周期》中最前沿的分类和研究，一个周期通常可以分为四个阶段，大致包括： Expansion: A speedup in the pace of economic activity defined by high growth, low unemployment, and increasing prices. The period marked from trough to peak. 扩张：经济增长速度加快，由高增长、低失业率和物价上涨所决定。包括从低谷到高峰的时期。 Peak: The upper turning point of a business cycle and the point at which expansion turns into contraction. 峰值：商业周期的上升拐点和收缩拐点。 Contraction: A slowdown in the pace of economic activity defined by low or stagnant growth, high unemployment, and declining prices. It is the period from peak to trough. 收缩：经济活动放缓，由低增长或停滞增长，高失业率和价格下降所决定。包括从峰值到低谷的时期。 Trough: The lowest turning point of a business cycle in which a contraction turns into an expansion. This turning point is also called Recovery. 低谷：商业周期中收缩转变为扩张的最低拐点。这个拐点也称为复苏。 These four phases also make up what is known as the " boom- and- bust" cycles, which are characterized as business cycles in which the periods of expansion are swift and the subsequent contraction is steep and severe. 这四个阶段也构成了所谓的“繁荣与萧条”周期，其特征扩张迅速，收缩陡峭的商业周期。
But What About Recessions?