Monopoly is defined as a market situation where there is a single seller with complete control over an industry. Key features of monopoly include a single seller, price discrimination, lack of close substitutes, and restricted market entry. True monopolies generally exist in government controlled markets or through legal barriers like patents and copyrights that provide opportunities to monopolize a market. The Tata Nano is an example of a monopoly in its market segment as Tata is the only seller and there are no close substitutes, along with barriers to entry.