A monopoly, as described by Irving Fisher, is a market with the "absence of competition", creating a situation where a specific person or enterprise is the only supplier of a particular thing. 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 and duopoly which consists of a few sellers dominating a market. Monopolies are thus characterised 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, which is associated with unfair price raises. 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.

अर्थशास्त्रात जेव्‍हा एका व्यक्ति अथवा संस्थेचे एखाद्या उत्पादनावर अथवा सेवेवर एवढे नियंत्रण होते कि ती व्यक्ति अथवा संस्था विक्रीसंबंधित अटी व मूल्य आपल्या इच्छेनुसार लागू करू शकते अशी स्थिति म्हणजे एकाधिकार अथवा मक्तेदारी. "मोनॉपली" ह्या संज्ञेचा वापर सर्वप्रथम ग्रीक तत्त्वज्ञ अ‍ॅरिस्टॉटलने त्याच्या "पॉलिटिक्स" नामक ग्रंथात केला होता. मात्र काळानुरूप त्याचे संदर्भ आणि अर्थ बदलत गेले.