Explain imperfect competition and distinguish between its main types: monopoly, oligopoly, and monopolistic competition.

Imperfect competition describes market structures where individual firms have some control over the price of their products, unlike in perfect competition. This occurs due to factors such as product differentiation, barriers to entry, or a limited number of sellers.

The main types are monopoly, oligopoly, and monopolistic competition. A monopoly features a single seller of a unique product with high barriers to entry. An oligopoly involves a few large firms dominating the market, often with interdependent decision-making and significant barriers to entry. Monopolistic competition is characterized by many firms selling differentiated products with relatively low barriers to entry.