Imperfect markets do not meet the strict standards of a hypothetical perfectly or purely competitive market.
Imperfect markets are characterized by competition for market share, high barriers to entry and exit, a variety of goods and services, and few buyers and sellers.
Perfect markets are theoretical and cannot exist in the real world; all real world markets are imperfect.
Imperfect market structures include monopolies, oligopolies, monopolistic competition, monopsony and oligopsony.