Which market structure is characterized by a single producer or seller for a product?

The market structure characterized by a single producer or seller for a product is a monopoly. In this type of market, one firm dominates the entire market and is the sole provider of a particular product or service. This firm has significant control over the prices and supply because there are no direct competitors. The absence of competition allows a monopolist to set prices above marginal costs, potentially leading to higher profits.

Monopolies can arise due to various factors, including ownership of a key resource, patents, or government regulations that restrict competition. This structure contrasts sharply with others, such as perfect competition, where many sellers exist; oligopoly, which has a few large firms; and monopsony, where a single buyer controls the market. Understanding monopolies is crucial because they can have significant implications for pricing, consumer choice, and overall market efficiency.