This document discusses oligopoly, which is a market structure with a small number of sellers offering similar or differentiated products. It begins by defining oligopoly and providing some examples, such as automobiles, cement, and steel industries in India. The document then outlines the two main types of oligopoly - collusive, where firms cooperate to maximize profits, and non-collusive, where firms compete independently. Key characteristics of oligopoly markets are the small number of firms, interdependent decision-making, importance of advertising, barriers to entry, and unpredictable prices and output levels.