通货膨胀（简称“通胀”）一般指：在纸币流通条件下，因货币供给大于货币实际需求，也即现实购买力大于产出供给，导致货币贬值，而引起的一段时间内物价持续而普遍地上涨现象。
Inflation generally refers to: under the condition of paper currency circulation, the currency supply is greater than the actual demand for currency, that is, the actual purchasing power is greater than the output supply, resulting in currency depreciation, which causes the phenomenon of continuous and general price increases over a period of time.
在宏观经济学中，通胀主要是指价格和工资的普遍上涨。通货膨胀之反义为通货紧缩。
In macroeconomics, inflation mainly refers to the general rise in prices and wages. The antonym of inflation is deflation.
通胀和一般物价上涨是有本质区别的：后者是指一种或几种商品因为供求失衡而造成物价上涨，其上涨是局部、暂时、可逆的，不会造成货币贬值；通胀则是能够造成一国货币贬值，其国内主要商品物价上涨是普遍的、持续的、不可逆的。
产生通胀的原因：在凯恩斯主义经济学中，认为经济体中总供给与总需求的变化导致物价水平的移动；在货币主义经济学中，认为当市场上货币发行量超过流通中所需要的货币量，就会出现纸币贬值，物价上涨，导致购买力下降，该理论被总结为一个非常著名的方程：MV=PT。
综观不同的经济学派理论货币扩张是否带来通胀，主要看货币的创造模式，财政投放货币一般会推升通胀，而私人部门信贷投放货币一般会推升资产价格。1930至1980年，美国广义货币与通胀水平同时增长，广义货币平均增速为6.9%，通胀平均值为3.2%。1981至2019年，美国广义货币保持增长，但是通胀水平下行，广义货币平均增速为6.0%，通胀平均值为2.8%。
通胀始终受到宏观政策研究、资本市场的高度关注，在对经济形势和资本市场的分析体系之中具有极其重要的地位，与货币政策的走向也存在着非常紧密的联系。
通货紧缩（简称“通缩”），是一个与通货膨胀相对应的经济学概念，是由货币供给量相对于经济增长和劳动生产率提高等要素减少而引致的有效需求严重不足，一般物价水平持续下跌，货币供给量持续下降和经济衰退的现象。当市场上流通的货币减少，人民的货币所得减少，购买力下降，导致物价下跌，造成通货紧缩。长期的货币紧缩会抑制投资与生产，导致失业率升高及经济衰退。
通货紧缩按照指标数值划分，可分为相对通货紧缩和绝对通货紧缩；按照对经济的影响程度划分，可分为轻度通货紧缩、中度通货紧缩和严重通货紧缩；按供求量来划分，则可分为需求不足型通货紧缩和供给过剩型通货紧缩。经济学者主要通常将通货紧缩归纳为4种类型：1、欧文·费雪提出的债务性通缩；2、货币主义者认为的货币供给性通缩；3、本·伯南克提出的信贷性通缩；4、凯恩斯提出的流动性陷阱和有效需求不足。
历史上，美国曾发生过几次典型的通货紧缩，对经济影响程度最大的一次发生在1929-1933年”大萧条”时期。在此期间，美国物价下降了227%，货币数量年均遗减10%，银行数目减少了42%，实际国民生产总值下降了30%。2008年国际金融危机以来，通货紧缩和经济下行日益成为世界经济面临的新问题，通货紧缩对经济生活产生了各种消极影响。
There is an essential difference between inflation and general price increases: the latter refers to the price increase of one or several commodities due to the imbalance of supply and demand. The increase is local, temporary, and reversible, and will not cause currency depreciation; inflation can cause a country’s currency to depreciate, and the price increase of its main domestic commodities is universal, continuous, and irreversible.
Causes of inflation: In Keynesian economics, it is believed that changes in total supply and total demand in an economy lead to the movement of price levels; in monetarist economics, it is believed that when the amount of money issued in the market exceeds the amount of money needed in circulation, paper currency will depreciate, prices will rise, and purchasing power will decline. This theory is summarized as a very famous equation: MV=PT.
Looking at the theories of different economic schools, whether monetary expansion will bring inflation depends mainly on the money creation model. Fiscal money supply generally pushes up inflation, while private sector credit money supply generally pushes up asset prices. From 1930 to 1980, the broad money and inflation levels in the United States grew simultaneously, with an average growth rate of 6.9% and an average inflation rate of 3.2%. From 1981 to 2019, the broad money in the United States continued to grow, but the inflation level declined, with an average growth rate of 6.0% and an average inflation rate of 2.8%.
Inflation has always been highly concerned by macroeconomic policy research and the capital market. It has an extremely important position in the analysis system of the economic situation and the capital market, and is also closely related to the direction of monetary policy.
Deflation (abbreviated as “deflation”) is an economic concept corresponding to inflation. It is a phenomenon of severe insufficient effective demand, continuous decline in general price levels, continuous decline in money supply and economic recession caused by the reduction of money supply relative to economic growth and labor productivity. When the amount of money in circulation in the market decreases, people’s monetary income decreases, and purchasing power decreases, leading to falling prices and deflation. Long-term monetary deflation will inhibit investment and production, leading to higher unemployment and economic recession.
Deflation can be divided into relative deflation and absolute deflation according to the index value; it can be divided into mild deflation, moderate deflation and severe deflation according to the degree of impact on the economy; it can be divided into insufficient demand deflation and excess supply deflation according to supply and demand. Economists usually classify deflation into four types: 1. Debt deflation proposed by Irving Fisher; 2. Monetarists believe in monetary supply deflation; 3. Credit deflation proposed by Ben Bernanke; 4. Liquidity trap and insufficient effective demand proposed by Keynes.
Historically, the United States has experienced several typical deflations, and the one with the greatest impact on the economy occurred during the “Great Depression” from 1929 to 1933. During this period, US prices fell by 227%, the amount of money decreased by an average of 10% per year, the number of banks decreased by 42%, and the real GDP fell by 30%. Since the international financial crisis in 2008, deflation and economic downturn have increasingly become new problems facing the world economy, and deflation has had various negative effects on economic life.