Economics is the study of how society manages scare resources. It is a wide branch of the social sciences that studies how the billions of people, companies, and organizations throughout the world make decisions; it studies "the economy". The economy is partially driven by scarcity of resources, limitations in how much their are of certain goods and who can have those goods.
Generally, economics is divided between Microeconomics and Macroeconomics, with "micro" as its colloquially called, focusing on the decision making of individual agents (people, families, firms, etc.) given their limited resource. "Macro" looks broadly, at economies as a whole (the economy of a country, an industry, countries that trade, etc.).
Goods and Services are the items that are bought and sold in an economy. Typically goods are thought of as tangible products - food, clothing, cell phones, etc. Services are activities performed for a person - for instance a doctor performing surgery, a barber cutting hair, an accountant doing taxes, etc.
Markets are groups of buyers and sellers for particular goods and services. This could be a physical marketplace, for instance for fruits and vegetables. A digital one, like eBay or Amazon. A financial one, like stock markets. Or any other place where someone buys something and another person sells it.
A price is the amounts of money demanded in exchange for a good or service. Prices are a reflection of the value of that good or service, but may be inflated beyond the true value of the good or service, or deflated below the costs that went in to produce the good or service.
Efficiency means to get the most one can from scarce resources. It is about reducing waste, and maximizing value.
Supply and Demand
Main Article: Supply and Demand
Supply and Demand are two primary forces in markets. Supply and demand graphs help show why prices rise quickly for apartments in markets where there is a lot of demand (but little supply!), like San Francisco; or how prices for a good like oil can fall when refiners discover new oil deposits, increase production, or release millions of barrels of crude oil they held in reserve. But supply and demand graphs are not only limited to prices, they can represent decreases in wages when there is high unemployment, why some restaurants are booked out months in advance, or how interest rates affect the supply of money.
The equilibrium is the point where supply and demand for a product meet. It is the point where consumer demand for a good at various prices meets the price suppliers are willing to accept to produce the desired quantity of that good. Equilibrium means balance, and when markets become unbalanced (for instance consumers demand more of a good than is currently being supplied) then markets tend to shift back to equilibrium (either suppliers raise prices, increase production, or both - generally both - to meet the increase in demand).
Elasticity is a measure of responsiveness - specifically how responsive quantity supplied or quantity demanded is to a change. This could be a change in price, with suppliers raising their prices, in which case a measure of consumer's reaction would be referred to as their price elasticity. Demand or supply are said to be price elastic if they respond substantially to changes in price, and price inelastic if they respond only slightly.
Governments can significantly affect the price of goods sold, seller behaviors, or consumer behaviors. For instance, governments can fix prices, setting the maximum price at a certain amount, known as a price ceiling. Or they can favor suppliers, setting a minimum price that goods can be sold at, known as a price floor. Governments can also limit how much prices can increase, or penalizing sellers who charge more or less than they're supposed to charge.
Main Article: externalities
Externalities are a cost or a benefit that occurs to a bystander. For instance, a factory may pollute the air in it's town. The company running the factory may not have to pay for the costs of this pollution, nor may the customers that buy the factory's products. However, the people who live in that town are bystanders that pay for the cost of the pollution. Externalities can be positive or negative, and occur on the supply side or the demand side. As an example, some forms of construction produce positive externalities. Building a new luxury high-rise condominium in a neighborhood can bring in more customers (the new residents) to local businesses (a positive supply-side externality) and might raise property values (a positive demand-side externality).
Main Article: utility functionsCompetition, Monopolies, Oligopolies
Growth: Economic, Population, Technological
Aggregate Supply and Demand (IS-LM)
Monetary Supply and Banking
Main Article: game theory
Game theory is the mathematical analysis of decision making. In game theory, the interaction between two or more players is often framed in terms of a game with a particular set of rules. Of interest may be the strategies that give optimal outcomes for each of the players or, conversely, the resulting outcomes when certain strategies are played. The prisoner's dilemma is one of the more famous "games" that economist have tested.