A monopoly refers to a market with a single supplier or producer; many buyers, it's controlled by the government regulations and has barriers to entry and exit.

The electricity industry is one of the best examples of a monopoly industry. In the United States, telephone service is provided by a single industry.

What about an oligopoly?

An oligopoly is a structure with a few large firms that can operate individually without restricting other firms' from influencing the market. The structure has barriers to entry and exit, and the sellers can sell similar or differentiated products.

The automobile industry is the best example of an industry under the oligopoly market structure.

What about monopolistic competition?

Monopolistic competition has several characteristics including many buyers and sellers, few or no barriers to entry and exits, and all buyers and sellers are well informed about the products in the market.

The best example of an industry under monopolistic competition is the electronics industry, in which consumers and sellers are well informed of the quality and prices of electronics.