A monopoly refers to a market structure where only one seller or producer serves the entire market for a particular product or service. In such a scenario, the monopolist holds significant control over the supply and price of the product, facing no competition from other sellers. A monopoly firm typically offers a unique or differentiated product with no close substitutes. The monopolist can influence market price by adjusting output.

There are some common market characteristics that cause monopolies to emerge:

1. Legal Barriers: Patents, copyrights, or government regulations.

2. Control of Resources: Exclusive access to key inputs or technologies.

3. Economies of Scale: When average costs decrease as output increases, making it difficult for smaller firms to compete. (This is often called a natural monopoly.)

4. Network Effects: The value of a product increases as more people use it for example., social media platforms.

An example of a monopoly is Microsoft's Windows, which dominates the market for PC operating systems with minimal competition. Similarly, De Beers historically held a monopoly over the diamond industry, controlling most diamond production and distribution worldwide.

Furthermore, all monopolies are not necessarily bad for society. For example, in the United States, public utilities such as local water and electricity suppliers are often natural monopolies. They are sometimes given monopoly status in a specific market to preserve efficient delivery of utility services. Further, some monopolies can use monopoly market power to foster technological innovation or provide key services in markets where competition is not possible.