1. An economic situation in which two powerful groups or organizations concentrate or dominate commerce in one business market or commodity.
2. A condition in which there are only two suppliers of a particular commodity, service, etc.; the domination of a particular market by two firms.
3. A situation in which two companies own all or nearly all of the market for a given type of product or service.
4. An economic or political condition in which power is concentrated in two persons or groups.

A true duopoly is another form of oligopoly where only two producers exist in a market. By definition, it refers to two firms which have dominant control over a market. In the field of industrial organization, it is considered to be the most commonly known form of oligopoly.