In economics, a market with one seller and many buyers is called a monopoly.
A monopolist supplies the market and faces the market demand curve, unlike a perfectly competitive firm that treats market price as given. Because there is no competing seller offering a close substitute within the defined market, the monopolist may have market power and can influence price by choosing output.
A monopoly can arise from legal barriers, control of an essential resource, economies of scale, or network effects. A government-granted patent is one example of a temporary legal barrier, while a natural monopoly can occur when one large provider has lower average costs than several smaller providers.
Monopoly does not simply mean a large or successful company. The definition depends on the relevant market and on whether effective substitutes and competing suppliers exist.