average revenue  total revenue divided by quantity.
barriers to entry  anything that prevents firms from entering a market.
contestable market  a market in which the threat of competition is enough to encourage firms to act like competitors.
market power  a firm’s power to set its price without losing its entire share of the market.
monopoly  one firm in an industry selling a product for which there are no close substitutes.
natural monopoly  a single firm in an industry in which average total cost is declining over the entire range of production and the minimum efficient scale is larger than the size of the market.
price discrimination  a situation in which different groups of consumers are charged different prices for the same good.