Which best defines a monopoly?

A monopoly is defined as a market structure where a single seller dominates the entire market. This means that the monopolist has significant control over the price and supply of the product or service offered, as there are no close substitutes available. In a monopoly, the lack of competition allows the seller to influence market conditions to a greater extent than in other market structures.

This dominance can arise due to various factors such as exclusive control over a resource, government regulations, or significant barriers to entry that prevent other firms from entering the market. Unlike other market structures where multiple firms compete, a monopoly restricts competition, leading to less consumer choice and potentially higher prices for consumers.