The document discusses market structure and defines its key characteristics. It presents a spectrum ranging from perfect competition to pure monopoly based on the degree of competition. Perfect competition has many small firms, homogeneous products, free entry and exit, and firms as price takers. Pure monopoly is at the other end with a single firm, no good substitutes, and barriers to entry. In between are monopolistic competition and oligopoly. The characteristics and models are described to analyze real world industries.