A market is where buyers and sellers can meet to potentially transact the buying and selling of goods and services. In economics, a market refers not to a physical place but to the interactions between buyers and sellers of a particular commodity. Markets can be classified based on their geographic scope (local, national, international), time period of supply adjustment (very short, short, long, very long), and degree of competition (perfect competition, monopoly, duopoly, oligopoly, monopsony, monopolistic competition). A perfectly competitive market has many small buyers and sellers of identical goods, free entry and exit of firms, and prices determined by supply and demand.