Parkin and Bade's text Economics gives the following definition of the business cycle:
在帕金和巴德的經(jīng)濟學教材中，對商業(yè)周期給出了以下定義：

"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."
“商業(yè)周期是經(jīng)濟活動的周期性但不規(guī)則的上下波動，以實際GDP和其他宏觀經(jīng)濟變量的波動來衡量?！?/span>

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.
簡單地說，商業(yè)周期是指經(jīng)濟活動和國內(nèi)生產(chǎn)總值在一段時間內(nèi)的實際波動。經(jīng)濟在活動中經(jīng)歷這些起起落落的事實不足為奇。事實上，所有像美國那樣的現(xiàn)代工業(yè)經(jīng)濟體，隨著時間的推移，經(jīng)濟活動都會出現(xiàn)相當大的波動。

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.
高增長和低失業(yè)率等指標可能標志著經(jīng)濟復蘇，而經(jīng)濟低迷通常由低增長或停滯增長以及高失業(yè)率來定義。鑒于失業(yè)與商業(yè)周期各階段的關系，失業(yè)只是用來衡量經(jīng)濟活動的各種經(jīng)濟指標之一。有關各種經(jīng)濟指標及其與商業(yè)周期的關系的最詳細信息，請參閱《經(jīng)濟指標入門指南》。

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.
帕金和巴德繼續(xù)解釋道，盡管名字中有周期二字，但商業(yè)周期并不是一個規(guī)律的、可預測的或重復的循環(huán)。雖然它的階段可以被定義，但其時間是隨機的，并且在很大程度上是不可預測的。

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The Phases of the Business Cycle
商業(yè)周期的各個階段

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:
雖然沒有兩個商業(yè)周期是完全相同的，而根據(jù)美國經(jīng)濟學家阿瑟?伯恩斯和衛(wèi)斯理?米切爾在他們的著作《衡量商業(yè)周期》中最前沿的分類和研究，一個周期通常可以分為四個階段，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.
擴張：經(jīng)濟增長速度加快，由高增長、低失業(yè)率和物價上漲所決定。包括從低谷到高峰的時期。

Peak: The upper turning point of a business cycle and the point at which expansion turns into contraction.
峰值：商業(yè)周期的上升拐點和收縮拐點。

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.
收縮：經(jīng)濟活動放緩，由低增長或停滯增長，高失業(yè)率和價格下降所決定。包括從峰值到低谷的時期。

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：商業(yè)周期中收縮轉(zhuǎn)變?yōu)閿U張的最低拐點。這個拐點也稱為復蘇。

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.
這四個階段也構成了所謂的“繁榮與蕭條”周期，其特征擴張迅速，收縮陡峭的商業(yè)周期。

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But What About Recessions?
但是經(jīng)濟衰退呢？

A recession occurs if a contraction is severe enough. The National Bureau of Economic Research (NBER) identifies a recession as a contraction or significant decline in economic activity "lasting more than a few months, normally visible in real GDP, real income, employment, industrial production."
如果收縮足夠嚴重，就會出現(xiàn)衰退。美國國家經(jīng)濟研究局認為經(jīng)濟衰退是經(jīng)濟活動的收縮或顯著下降“持續(xù)幾個月以上，通?？梢娪趯嶋HGDP、實際收入、就業(yè)和工業(yè)生產(chǎn)中?！?/span>

Along the same vein, a deep trough is called a slump or a depression. The difference between a recession and a depression, which is not well-understood by non-e·conomists, is explained in this helpful guide: Recession? Depression? What's the difference?
同樣的情況下，一個深谷被稱為暴跌或蕭條。經(jīng)濟衰退和蕭條之間的差別，非經(jīng)濟學家不太了解，在這本實用指南中解釋了：衰退？蕭條？有什么區(qū)別？

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The Great Recession
經(jīng)濟大衰退

The Great Recession was a period of general economic decline observed in world markets during the late 2000s and early 2010s.
“大衰退”指的是20世紀末至2010年初全球市場普遍出現(xiàn)的經(jīng)濟衰退時期。

The scale and timing of the recession varied from country to country. The International Monetary Fund concluded that the overall impact was the most severe since the Great Depression in the 1930s.
經(jīng)濟衰退的規(guī)模和時機因國而異。國際貨幣基金組織得出的結論是，自上世紀30年代大蕭條以來，“大衰退”的總體影響最為嚴重。

The Great Recession stemmed from collapse of the United States real-estate market, in relation to the financial crisis of 2007 to 2008 and U.S. subprime mortgage crisis of 2007 to 2009, though policies of other nations contributed also. According to the U.S. National Bureau of Economic Research (the official arbiter of U.S. recessions) the US recession began in December 2007 and ended in June 2009, thus extending over 19 months.
大蕭條源于美國房地產(chǎn)市場的崩潰，與2007-2008年的金融危機和2007-2009年的美國次貸危機有關，盡管其他國家的政策也起到了一定作用。根據(jù)美國國家經(jīng)濟研究局（美國經(jīng)濟衰退的官方仲裁機構）的數(shù)據(jù)，美國經(jīng)濟衰退始于2007年12月，結束于2009年6月，持續(xù)了19個月的時間。

The Great Recession resulted in the scarcity of valuable assets in the market economy and the collapse of the financial sector (banks) in the world economy. The banks were then bailed out by the U.S. government.
大蕭條導致了市場經(jīng)濟中寶貴資產(chǎn)的稀缺和世界經(jīng)濟中金融部門（銀行）的崩潰。隨后這些銀行得到了美國政府的救助。

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（翻譯：雅蘭）