Single Supplier: The essence of a monopoly is a market controlled by a single seller. The "mono" part of monopoly means single. The "poly" part of monopoly means to sell. So the word itself, monopoly, means a single seller.
Unique Product: To be the only seller of a product, however, a monopoly must have a unique product.
Barriers to Entry and Exit: A monopoly is generally assured of being the ONLY firm in a market because of assorted barriers to entry. Some of the key barriers to entry are: Government License or franchise, Resource Ownership, Parents and copyrights, High start-up cost, and Decreasing average total cost.
Specialized Information: Monopoly is commonly characterized by control of information or production technology not available to others. This specialized information often comes in the form of legally-established patents, copyrights, or trademarks.