Oligopoly:A market structure characterized by a small number of firms that have a significant influence over the market, leading to interdependent decision-making and strategic interactions among the firms.
Herfindahl-Hirschman Index (HHI): A measure of market concentration that takes into account the relative size of all firms in a market, calculated by summing the squares of the market shares of each firm.
Concentration Ratio (CR): A measure of market concentration that calculates the combined market share of the largest firms in a market, typically the top 4 or 8 firms.