商業週期包括哪幾個階段?

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

"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."
“商業週期是經濟活動的週期性但不規則的上下波動，以實際GDP和其他宏觀經濟變量的波動來衡量。”

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.
簡單地說，商業週期是指經濟活動和國內生產總值在一段時間內的實際波動。經濟在活動中經歷這些起起落落的事實不足爲奇。事實上，所有像美國那樣的現代工業經濟體，隨着時間的推移，經濟活動都會出現相當大的波動。

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.
高增長和低失業率等指標可能標誌着經濟復甦，而經濟低迷通常由低增長或停滯增長以及高失業率來定義。鑑於失業與商業週期各階段的關係，失業只是用來衡量經濟活動的各種經濟指標之一。有關各種經濟指標及其與商業週期的關係的最詳細信息，請參閱《經濟指標入門指南》。

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.
帕金和巴德繼續解釋道，儘管名字中有周期二字，但商業週期並不是一個規律的、可預測的或重複的循環。雖然它的階段可以被定義，但其時間是隨機的，並且在很大程度上是不可預測的。

The Phases of the Business Cycle
商業週期的各個階段

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:
雖然沒有兩個商業週期是完全相同的，而根據美國經濟學家阿瑟·伯恩斯和衛斯理·米切爾在他們的著作《衡量商業週期》中最前沿的分類和研究，一個週期通常可以分爲四個階段，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：經濟增長速度加快，由高增長、低失業率和物價上漲所決定。包括從低谷到高峯的時期。

Peak: The upper turning point of a business cycle and the point at which expansion turns into contraction.
峯值：商業週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：經濟活動放緩，由低增長或停滯增長，高失業率和價格下降所決定。包括從峯值到低谷的時期。

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：商業週期中收縮轉變爲擴張的最低拐點。這個拐點也稱爲復甦。

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”週期，其特徵擴張迅速，收縮陡峭的商業週期。

But What About Recessions?
但是經濟衰退呢？

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，就會出現衰退。美國國家經濟研究局認爲經濟衰退是經濟活動的收縮或顯著下降“持續幾個月以上，通常可見於實際GDP、實際收入、就業和工業生產中。”

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-economists, is explained in this helpful guide: Recession? Depression? What's the difference?
同樣的情況下，一個深谷被稱爲暴跌或蕭條。經濟衰退和蕭條之間的差別，非經濟學家不太瞭解，在這本實用指南中解釋了：衰退？蕭條？有什麼區別？

The Great Recession
經濟大衰退

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的經濟衰退時期。

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.
經濟衰退的規模和時機因國而異。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”的總體影響最爲嚴重。

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.
大蕭條源於美國房地產市場的崩潰，與2007-2008年的金融危機和2007-2009年的美國次貸危機有關，儘管其他國家的政策也起到了一定作用。根據美國國家經濟研究局（美國經濟衰退的官方仲裁機構）的數據，美國經濟衰退始於2007年12月，結束於2009年6月，持續了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濟中寶貴資產的稀缺和世界經濟中金融部門（銀行）的崩潰。隨後這些銀行得到了美國政府的救助。