What market condition exists when one business controls the supply of a product?

The condition described in the question is a monopoly. In a monopoly, a single business or entity has complete control over the production and distribution of a particular product or service in a market, which allows it to dominate prices and supply. This lack of competition can lead to higher prices for consumers and less innovation in the market, as the monopolist faces no significant rivalry.

In contrast, an oligopoly consists of a few companies that dominate a market, which can lead to competitive behaviors among them. Competition refers to a market condition where multiple businesses vie for the same customers, promoting lower prices and variety. A duopoly specifically is a market structure dominated by two firms, which can also lead to competitive practices but not to the extent of a monopoly. Understanding these distinctions highlights the unique characteristics of each market structure and the implications of having varying degrees of competition.