Monopoly can best be described as a market in which

A monopoly is a market structure in which there is only one seller (or producer) of a product that has no close substitutes. Because the monopolist is the sole supplier, it has significant control over the price and output of the product. Consumers cannot switch to an alternative because no closely comparable product exists.

Key characteristics of a monopoly include:

• A single firm constitutes the entire industry.
• The product is unique with no close substitutes.
• There are high barriers to entry that prevent other firms from entering the market.
• The monopolist is a price maker, not a price taker.

The description of entry being restricted by a few firms in the market refers to an oligopoly, where a small number of large firms dominate. Two or more sellers selling differentiated products describes monopolistic competition. Few sellers selling at different prices also suggests an oligopolistic market. None of these match the defining feature of monopoly, which requires a single seller with a product that has no close substitute.