What is Monopoly?

Legal Definition
A monopoly (from Greek μόνος mónos ("alone" or "single") and πωλεῖν pōleîn ("to sell")) exists when a specific person or enterprise is the only supplier of a particular commodity (this contrasts with a monopsony which relates to a single entity's control of a market to purchase a good or service, and with oligopoly which consists of a few sellers dominating a market.) Monopolies are thus characterized by a lack of economic competition to produce the good or service, a lack of viable substitute goods, and the possibility of a high monopoly price well above the seller's marginal cost that leads to a high monopoly profit. The verb monopolise or monopolize refers to the process by which a company gains the ability to raise prices or exclude competitors. In economics, a monopoly is a single seller. In law, a monopoly is a business entity that has significant market power, that is, the power to charge overly high prices. Although monopolies may be big businesses, size is not a characteristic of a monopoly. A small business may still have the power to raise prices in a small industry (or market).

A monopoly is distinguished from a monopsony, in which there is only one buyer of a product or service; a monopoly may also have monopsony control of a sector of a market. Likewise, a monopoly should be distinguished from a cartel (a form of oligopoly), in which several providers act together to coordinate services, prices or sale of goods. Monopolies, monopsonies and oligopolies are all situations in which one or a few entities have market power and therefore interact with their customers (monopoly or oligopoly), or suppliers (monopsony) in ways that distort the market.

Monopolies can be established by a government, form naturally, or form by integration.

In many jurisdictions, competition laws restrict monopolies. Holding a dominant position or a monopoly in a market is often not illegal in itself, however certain categories of behavior can be considered abusive and therefore incur legal sanctions when business is dominant. A government-granted monopoly or legal monopoly, by contrast, is sanctioned by the state, often to provide an incentive to invest in a risky venture or enrich a domestic interest group. Patents, copyrights, and trademarks are sometimes used as examples of government-granted monopolies. The government may also reserve the venture for itself, thus forming a government monopoly.
-- Wikipedia
Legal Definition
A type of commercial advantage enjoyed by one business entity that lets it determine to a significant extent the terms on which products or services may be obtained in a given region. For example, a monopoly would exist if a single supplier of gasoline in a state could significantly hike prices without serious competition.

See Antitrust Law for more information.
Legal Definition
Commercial law. This word has various significations. 1. It is the abuse of free commerce by which one or more individuals have procured the advantage of selling alone all of a particular kind of merchandise, to the detriment of the public.

2. - 2. All combinations among merchants to raise the price of merchandise to the injury of the public, is also said to be a monopoly.

3. - 3. A monopoly is also an institution or allowance by a grant from the sovereign power of a state, by commission, letters patent, or otherwise, to any person, or corporation, by which the exclusive right of buying, selling, making, working, or using anything, is given. Bac. Abr. h. t.; 3 Inst. 181.

4. The constitutions of Maryland, North Carolina, and Tennessee, declare that "monopolies are contrary to the genius of a free government, and ought not to be allowed." Vide art. Copyyright; Patent.
-- Bouviers Law Dictionary
Legal Definition
In commercial law. A privilege or peculiar advantage vested in one or more persons or companies, consisting in the exclusive right (or power) to carry on a particular business or trade, manufacture a particular article or control the sale of the whole supply of a particular commodity. Defined in English law to be "a license or privilege allowed by the king for the sole buying and selling, making, working, or using, of anything whatsoever; whereby the subject in general is restrained from that liberty of manufacturing or trading which he had before." 4 Bl. Comm. 159; 4 Steph. Comm. 291. And see State v. Duluth Board of Trade, 107 Minn. 506, 121 N. W. 395, 23 L. R. A. (N. S'.) 1260. A monopoly consists in the ownership or control of so large a part of the market-supply or output of a given commodity as to stifle competition, restrict the freedom of commerce, and give the monopolist control over prices. See State v. Eastern Coal Co., 29 R. I. 254, 70 Atl. 1, 132 Am. St. Rep. 817; Over v. Byram Foundry Co., 37 Ind. App. 452,'77 N. E. 302, 117 Am. St. Rep. 327; State v. Haworth, 122 Ind. 462, 23 N. E. 946, 7 L. In A. 240; Davenport v. Kleinschmidt, 6 Mont. 502, 13 Pac. 249; Ex parte Levy, 43 Ark. 42, 51 Am. Rep. 550; Case of Monopolies, 11 Coke, 84; Laredo v. International Bridge, etc., Co., 66 Fed. 246, 14 C. C. A. 1; International Tooth Crown Co. v. Hanks Dental Ass'n (C. Ct) 111 Fed. 916; Queen Ins. Co. v. State, 86 Tex. 250, 24 S. W. 397, 22 L. R. A. 483; Herriman v. Menzies, 115 Cal. 16, 46 Pan. 730, 35 L. R. A. 318, 56 Am. St Rep. 81.
-- Black's Law Dictionary
Legal Definition
An exclusive right, granted to a few, of something which was before of common right. See 11 Pet. (U. S.) 420, 9 L. Ed. 773. See, also, 74 Am. St. Rep. 236, note.
-- Ballentine's Law Dictionary