Elasticity of substitution measures the ease with which one can switch between factors of production. The concept has a broad range of applications, from comparisons of labour and capital in firms, immigrant versus native workers in the labour market, to assessing ‘clean’ versus ‘dirty’ methods of production for environmental economics.

Externalities are costs (negative externalities) or benefits (positive externalities) of market transactions that are not reflected in the market price and that affect individuals who are not participating in the market. Depending on the allocation of property rights in the economy, the presence of externalities is addressed through negotiation between the affected parties and/or government intervention in the market.

Derivatives of functions are computed using differential calculus. They are widely applied in economic modelling to measure the effects and rates of change in economic variables, as well as to determine maximum and minimum values of functions.

Inequality in economics refers to the study of the (unequal) distribution of resources within a society. Usually when economists talk about inequality they mean income inequality, i.e., the unequal distribution of the total income in an economy among its citizens. Sometimes the term inequality is used in other contexts as e.g. wealth inequality or also inequality of opportunities or consumption.

The Gini-coefficient is a statistical measure of inequality that describes how equal or unequal income or wealth is distributed among the population of a country. It takes a value between 0 and 1, and a higher Gini-coefficient is associated with higher inequality.

Total utility refers to the overall or total level of happiness or satisfaction that a consumer experiences by consuming a certain amount of a good or service. While marginal utility measures the change in (total) utility of consuming one additional unit, total utility measures the total level of happiness associated with the consumption of a certain quantity of the good.

The net present value (NPV) is used in finance and economics to describe or measure today´s value of a stream of future payoffs or payments. Many decisions that we take will not only have immediate (financial) consequences, but will also lead to future expenses or revenues. For example, if you take out a loan or a mortgage you receive a one-time payment today from your bank and in return you will have to pay back the loan plus interest in monthly installments. An insurance company will receive monthly contributions from their clients but has to pay in case of an accident.

Perfect competition describes a market structure in which many sellers and buyers exchange a homogeneous good and no individual can influence the market price, i.e., buyers and sellers are price takers. In a perfectly competitive market total welfare (that is, the sum of consumer and producer surplus) is maximal.

A price ceiling, also called price cap, is the maximum price that a seller is allowed to charge for a particular good or service by law. It is an instrument of market regulation that governments may use to ensure that firms do not abuse their market power by charging consumers excessively high prices. Particularly, for goods which are considered a necessity such as water, electricity, or food, the government may establish price ceilings to protect consumers.

Price discrimination is a pricing strategy in which firms charge different prices for different units of the same physical good or service, either to different consumers or to the same consumer. By doing so firms can increase their profits compared to selling each unit of the good at the same price. If and how a firm can successfully price discriminate depends crucially on the information that the firm has about its customers and on the possibilities of the consumers to engage in arbitrage.

An Edgeworth box (named after Irish philosopher and economist Francis Ysidro Edgeworth, 1881) is a two-dimensional representation of a simple, closed economy consisting of two individuals and two items (or resources) that are finite in supply. Any feasible allocation of the items between the individuals is included as a dot in the box; the individuals’ preferences over the items are represented through indifference curves.

A Cobb-Douglas production function models the relationship between production output and production inputs (factors). It is used to calculate ratios of inputs to one another for efficient production and to estimate technological change in production methods.

Individuals derive utility from the consumption of goods and services, and choose these so as to maximise their utility under any given budget.

Pareto efficiency (or also Pareto optimality) is an important efficiency concept in economics used to evaluate or compare different allocations of resources, names after Italian economist Vilfredo Pareto (1848–1923). An allocation of resources is Pareto efficient if it cannot be modified to increase the wellbeing of one individual without diminishing the wellbeing of any other individual.

Marginal utility is the change in wellbeing (or change in total utility) that a person experiences if they consume one additional unit of a good or service. One of the most basic ideas in economics is that the consumption of goods and services changes our level of satisfaction or happiness (also referred to as utility). Often, we measure this change in satisfaction in monetary terms. If, for example, we want to know how much the wellbeing of a person changes if we give them a book (for free), we can simply ask this person how much he or she is willing to pay for the book.

A monopoly describes a market in which there is only one firm and it does not face any competition. A monopolist is a firm that offers a unique product or service without close substitutes and therefore does not have any competitors. This means that the monopolist faces the entire market demand and each customer interested in buying the product can choose whether to buy from the monopolist at the respective price or not to buy at all.

The prisoner's dilemma is a well-known game in non-cooperative game theory that highlights how the individually rational behaviour of 'players' can lead to an outcome that is suboptimal for all involved. It is a game that is often used to analyze the possibility of cooperation in situations where self-interested individuals interact strategically.

A market is in equilibrium if at the market price the quantity demanded is equal to the quantity supplied. The price at which the quantity demanded is equal to the quantity supplied is called the equilibrium price or market clearing price and the corresponding quantity is the equilibrium quantity.

Nash equilibrium is an important equilibrium or solution concept in non-cooperative game theory. A Nash equilibrium is a strategy profile (i.e. a strategy for each player) in which each player is playing a best response to the strategy of the other(s). More simply, a Nash equilibrium describes a situation in which each person acts optimally given the actions of the others, so that no one wants to change his or her action.

Marginal revenue (MR) measures the change in total revenue that occurs when a firm increases output by one unit, i.e., it is the extra income (or revenue) generated by selling one additional unit.

Trade barriers refer to the obstacles that are put in place by governments to limit free trade between national economies. Trade barriers are thus essentially interventions in markets that happen to operate internationally. Trade barriers include tariffs (taxes) on imports (and occasionally exports) and non-tariff barriers to trade such as import quotas, subsidies to domestic industry, embargoes on trade with particular countries (usually for geopolitical reasons), and licenses to import goods into the economy.

When the price ratio between items changes this can induce a change in consumption. The part of such a change in consumption that is attributable purely to the change in the price ratio (and not to the associated change in purchasing power) is known as the substitution effect. The remaining part of the change in consumption that is not directly due to the change in the price ratio but is rather brought about by the change in purchasing power is known as the income effect.

Where there is scarcity, choices must be made! Scarcity refers to the finite nature and availability of resources while choice refers to people’s decisions about sharing and using those resources. The problem of scarcity and choice lies at the very heart of economics, which is the study of how individuals and society choose to allocate scarce resources.

An oligopoly is a market in which there are only a few sellers of the item being traded. The decisions of one seller thus affect the decisions of the other sellers in the market.  Sellers compete strategically in the market by taking each other’s interests and actions into account.

The price elasticity of supply for an item A ηA measures how the quantity of the item supplied qA changes in response to a change in the item’s price pA