📚 AP Economics: A Glossary of Essential Terms | AP 经济学：重要术语释义汇编
Success in AP Economics hinges on a deep understanding of its core vocabulary. This glossary distills the essential microeconomic and macroeconomic terms you will encounter on the exam, with concise explanations designed to reinforce your learning and boost your confidence.
要在AP经济学中取得成功，关键在于深刻理解其核心术语。本汇编提炼了你在考试中会遇到的基本微观经济学和宏观经济学概念，并配以简洁的解释，旨在巩固你的学习、增强你的信心。
1. Scarcity and Opportunity Cost | 稀缺性与机会成本
Scarcity is the condition in which unlimited human wants exceed the limited resources available to satisfy them. This fundamental economic problem forces societies to make choices about how to allocate land, labor, capital, and entrepreneurship.
稀缺性是指人类无限的欲望超过了可用于满足这些欲望的有限资源。这一基本经济问题迫使社会必须就如何分配土地、劳动、资本和企业家才能做出选择。
Opportunity cost is the value of the next best alternative that must be forgone when a decision is made. It is not simply a monetary cost; it includes all benefits lost from the alternative not chosen.
机会成本是指做出某项决策时必须放弃的次优选择的最大价值。它不仅仅是货币成本，还包括从所放弃的选择中失去的所有收益。
The production possibilities curve (PPC) illustrates scarcity, trade-offs, and opportunity cost by showing the maximum combinations of two goods an economy can produce with existing resources and technology. Points inside the curve represent inefficiency, while points outside are unattainable.
生产可能性曲线 (PPC) 通过展示一个经济体在现有资源和技术下所能生产的两种商品的最大组合，阐明了稀缺性、权衡取舍和机会成本。曲线内部的点代表效率低下，外部的点则无法达到。
Opportunity Cost = Value of Next Best Alternative – Value of Chosen Option
机会成本 = 次优选择的价值 – 所选方案的价值
2. Demand and Supply | 需求与供给
The law of demand states that, ceteris paribus, as the price of a good rises, the quantity demanded falls, and vice versa. This inverse relationship is represented by a downward-sloping demand curve.
需求定律指出，在其他条件不变的情况下，商品价格上升，需求量下降，反之亦然。这种反向关系表现为向右下方倾斜的需求曲线。
A change in quantity demanded is a movement along the demand curve caused solely by a change in the good’s own price. A shift in demand occurs when a non-price determinant (income, tastes, prices of related goods, expectations, number of buyers) changes.
需求量的变动是指仅由商品自身价格变化引起的、沿需求曲线的移动。需求变动则是由非价格决定因素（收入、偏好、相关商品价格、预期、购买者数量）变化导致的整条需求曲线的位移。
The law of supply states that, ceteris paribus, as the price of a good rises, the quantity supplied rises. This positive relationship yields an upward-sloping supply curve. Market equilibrium occurs where quantity demanded equals quantity supplied, determining the equilibrium price and quantity.
供给定律指出，在其他条件不变的情况下，商品价格上升，供给量增加。这种正向关系使供给曲线向上倾斜。市场均衡出现在需求量等于供给量的位置，由此决定了均衡价格和均衡数量。
3. Elasticity | 弹性
Price elasticity of demand (PED) measures how responsive quantity demanded is to a change in price. It is calculated as the percentage change in quantity demanded divided by the percentage change in price. Using the midpoint method avoids different values depending on the direction of change.
需求价格弹性 (PED) 衡量需求量对价格变化的反应程度。它的计算是用需求量变动的百分比除以价格变动的百分比。使用中点法可以避免因变动方向不同而算出不同数值。
PED = [(Qd₂ – Qd₁) / ((Qd₂ + Qd₁)/2)] / [(P₂ – P₁) / ((P₂ + P₁)/2)]
PED = [(Qd₂ − Qd₁) / ((Qd₂ + Qd₁)/2)] / [(P₂ − P₁) / ((P₂ + P₁)/2)]
If |PED| > 1, demand is elastic (sensitive to price); if |PED| < 1, demand is inelastic; if |PED| = 1, it is unit elastic. Perfectly elastic demand is horizontal, while perfectly inelastic demand is vertical.
如果 |PED| > 1，需求富有弹性（对价格敏感）；如果 |PED| < 1，需求缺乏弹性；如果 |PED| = 1，为单位弹性。完全弹性需求是一条水平线，完全无弹性需求则是一条垂直线。
Cross-price elasticity of demand measures how the quantity demanded of one good responds to a price change in another. A positive value indicates substitute goods; a negative value indicates complements. Income elasticity of demand measures the sensitivity of demand to changes in consumer income, with positive values for normal goods and negative values for inferior goods.
需求交叉弹性衡量一种商品的需求量对另一种商品价格变化的反应程度。正值表明两种商品为替代品，负值表明为互补品。需求收入弹性衡量需求对消费者收入变化的敏感度，正常品的值为正，低档品的值为负。
4. Market Structures | 市场结构
Perfect competition is characterized by many small firms, identical products, perfect information, and free entry and exit. Firms are price takers who maximize profit where marginal cost equals market price (MC = P). In the long run, economic profit is zero.
完全竞争市场具有众多小企业、同质产品、完全信息和自由进出等特征。企业是价格接受者，在边际成本等于市场价格 (MC = P) 处实现利润最大化。长期中，经济利润为零。
Monopoly is a market with a single seller of a unique product with high barriers to entry. The monopolist is a price maker, facing a downward-sloping demand curve, and maximizes profit where marginal revenue equals marginal cost (MR = MC), producing less and charging a higher price than a competitive market.
垄断是指唯一卖者出售独特产品且存在高进入壁垒的市场。垄断者是价格制定者，面对向下倾斜的需求曲线，在边际收益等于边际成本 (MR = MC) 处实现利润最大化，产量低于完全竞争、价格高于完全竞争。
Monopolistic competition combines many firms with differentiated products and low barriers. Oligopoly is dominated by a few large interdependent firms, often engaging in strategic behavior like collusion or game theory decisions, with high barriers to entry.
垄断竞争市场拥有大量企业、差异化的产品和低进入壁垒。寡头市场由少数几家相互依赖的大企业主导，常出现合谋或博弈论决策等战略性行为，进入壁垒较高。
5. Market Failure and Externalities | 市场失灵与外部性
Market failure occurs when the free market fails to allocate resources efficiently, leading to either over- or under-production. Common sources include externalities, public goods, and asymmetric information.
市场失灵是指自由市场无法有效配置资源，导致生产过多或过少。常见的诱因包括外部性、公共物品和信息不对称。
A negative externality (e.g., pollution) imposes a cost on third parties not involved in the transaction, causing the market to overproduce. A positive externality (e.g., education) provides a benefit to third parties, leading to underproduction. Governments may intervene with taxes, subsidies, or regulations.
负外部性（如污染）给未参与交易的第三方带来了成本，导致市场过度生产。正外部性（如教育）给第三方带来益处，导致生产不足。政府可通过征税、补贴或管制进行干预。
Public goods are non-excludable and non-rivalrous, meaning people cannot be effectively excluded from use and one person’s use does not reduce availability to others. This leads to the free-rider problem, requiring government provision. Asymmetric information, where one party has more information than the other, can cause adverse selection or moral hazard.
公共物品具有非排他性和非竞争性，即无法有效阻止人们使用，且一人的使用不会减少对他人的可用量。这导致了搭便车问题，需要政府提供。信息不对称，即一方比另一方掌握更多信息，可能导致逆向选择或道德风险。
6. Macroeconomic Objectives and GDP | 宏观经济目标与国内生产总值
Macroeconomic policy aims to achieve stable economic growth, low unemployment, and low, stable inflation. Gross Domestic Product (GDP) is the primary measure of a country’s economic output—the market value of all final goods and services produced within a country in a given period.
宏观经济政策旨在实现稳定的经济增长、低失业率和低而稳定的通胀。国内生产总值 (GDP) 是衡量一国经济产出的主要指标——一国在特定时期内生产的全部最终产品和服务的市场价值。
Nominal GDP is measured at current prices, while real GDP is adjusted for inflation, allowing meaningful comparisons over time. Real GDP per capita divides real GDP by population, giving a rough indicator of the average standard of living. The business cycle depicts the short-run fluctuations in economic activity, featuring peaks, troughs, expansions, and recessions.
名义GDP按当期价格计算，实际GDP则经通胀调整，可进行有意义的跨期比较。人均实际GDP用实际GDP除以人口，是平均生活水平的一个粗略指标。经济周期描绘了经济活动的短期波动，包括高峰、低谷、扩张和衰退。
7. Unemployment and Inflation | 失业与通货膨胀
Unemployment is measured by the unemployment rate, which is the percentage of the labor force (those employed or actively seeking work) that is jobless. Frictional unemployment arises from normal job turnover; structural unemployment results from a mismatch between workers’ skills and job requirements; cyclical unemployment is due to downturns in the business cycle.
失业通过失业率来衡量，即劳动力（已就业或正在积极寻找工作的人）中失业者的百分比。摩擦性失业源于正常的岗位变动；结构性失业源于工人技能与岗位要求不匹配；周期性失业则由经济周期下行引起。
The natural rate of unemployment is the sum of frictional and structural unemployment, existing when the economy is at full employment. Inflation is a sustained increase in the general price level. The Consumer Price Index (CPI) tracks the cost of a fixed basket of goods, while the GDP deflator covers all domestically produced goods.
自然失业率是摩擦性失业与结构性失业之和，存在于经济处于充分就业状态时。通货膨胀指总体物价水平的持续上涨。消费者价格指数 (CPI) 追踪固定一篮子商品的成本，而GDP平减指数涵盖所有国内生产的商品。
Inflation Rate = (CPI₂ – CPI₁) / CPI₁ × 100
通货膨胀率 = (CPI₂ − CPI₁) / CPI₁ × 100
8. Aggregate Demand and Aggregate Supply | 总需求与总供给
Aggregate demand (AD) shows the total quantity of output (real GDP) that households, firms, the government, and foreign buyers will purchase at each price level. It slopes downward due to the wealth effect, interest-rate effect, and foreign trade effect. AD shifts with changes in consumption, investment, government spending, and net exports.
总需求 (AD) 显示了在每一价格水平上，家庭、企业、政府和外国购买者将购买的总产出量（实际GDP）。由于财富效应、利率效应和外贸效应，AD曲线向右下方倾斜。消费、投资、政府支出和净出口的变化会导致AD曲线位移。
Short-run aggregate supply (SRAS) slopes upward; nominal wages are sticky, so a higher price level raises profit margins and output. Long-run aggregate supply (LRAS) is vertical at the full-employment level of output, as all prices and wages adjust. Macroeconomic equilibrium occurs at the intersection of AD and SRAS (and LRAS in the long run).
短期总供给 (SRAS) 向右上方倾斜；名义工资具有粘性，因此更高的价格水平会提高利润率并增加产出。长期总供给 (LRAS) 在充分就业产出水平上是一条垂直线，因为所有价格和工资都能充分调整。宏观经济均衡位于AD曲线与SRAS曲线（及长期中的LRAS）的交点处。
A recessionary gap exists when equilibrium output is below full-employment output, indicating cyclical unemployment. An inflationary gap occurs when equilibrium output exceeds full-employment output, putting upward pressure on the price level.
当均衡产出低于充分就业产出时，存在衰退缺口，表明存在周期性失业。当均衡产出超过充分就业产出时，出现通胀缺口，给价格水平带来上行压力。
9. Fiscal and Monetary Policy | 财政与货币政策
Fiscal policy involves changes in government spending and taxation to influence the economy. Expansionary fiscal policy (increased G or lower taxes) aims to close a recessionary gap; contractionary fiscal policy (lower G or higher taxes) addresses an inflationary gap. Automatic stabilizers, like progressive taxes and unemployment benefits, adjust without new legislation.
财政政策通过改变政府支出和税收来影响经济。扩张性财政政策（增加政府支出或减税）旨在缩小衰退缺口；紧缩性财政政策（减少政府支出或增税）用于应对通胀缺口。自动稳定器，如累进税和失业救济，无需新立法即可自动调节。
Monetary policy is conducted by a central bank, which manipulates the money supply and interest rates. Expansionary monetary policy (buying bonds, lowering the discount rate or reserve requirement) increases money supply, lowers interest rates, and boosts investment and consumption. Contractionary policy does the opposite to curb inflation.
货币政策由中央银行执行，通过调控货币供给和利率来影响经济。扩张性货币政策（购买债券、降低贴现率或存款准备金率）增加货币供给，降低利率，刺激投资和消费。紧缩性货币政策则相反，以抑制通胀。
Money Multiplier = 1 / Reserve Requirement
货币乘数 = 1 / 存款准备金率
10. International Trade and Exchange Rates | 国际贸易与汇率
Comparative advantage explains why countries gain from trade: a country should specialize in producing goods for which it has a lower opportunity cost, even if it has an absolute disadvantage in all goods. Terms of trade must lie between the two nations’ opportunity cost ratios for mutual benefit.
比较优势解释了国家为何能从贸易中获益：一国应专门生产其机会成本较低的商品，即使它在所有商品上都具有绝对劣势。贸易条件必须处于两国机会成本比率之间，才能实现互利。
Trade barriers, such as tariffs (taxes on imports) and quotas (quantity limits), protect domestic industries but reduce total surplus by creating deadweight loss. A floating exchange rate is determined by supply and demand in the foreign exchange market. Appreciation of a currency makes exports more expensive and imports cheaper; depreciation has the opposite effect.
贸易壁垒，如关税（对进口商品征税）和配额（数量限制），虽能保护国内产业，但会带来无谓损失，减少总剩余。浮动汇率由外汇市场的供求决定。货币升值使出口变贵、进口变便宜；贬值则产生相反效果。
The balance of payments accounts record all transactions between a country and the rest of the world. The current account includes trade in goods and services, income, and transfers, while the financial account records capital flows such as purchases of financial assets.
国际收支账户记录了一国与世界上其他国家之间的所有交易。经常账户包括货物和服务贸易、收入及转移支付，而金融账户记录资本流动，如购买金融资产。
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