In which market structure does a single seller control the entire supply of a product?

A monopoly is characterized by a single seller that dominates the entire supply of a product or service in the market. This market structure allows the monopolist to set prices without competition, as they are the sole provider of the goods or services. This lack of competitive pressure can lead to higher prices and reduced output compared to more competitive markets. In a monopoly, barriers to entry are typically high, preventing other firms from entering the market and offering alternatives to consumers. This control over supply gives the monopolist significant power over the market and can influence prices and availability of the product significantly.