Final answer:
Existing markets are where customers are already being served by existing companies, often seen in monopolistic competitive markets, such as the diverse clothing stores in the Mall of America.
Step-by-step explanation:
The markets in which customers are already being served by one or more companies are known as Existing markets. In these markets, there is an established customer base and competition among firms. These scenarios are often observed in monopolistic competition, where numerous firms are in competition, but offering differentiated products. An example of a monopolistic competitive market is the Mall of America, with a variety of stores offering women's clothing, men's and women's clothing, and women's specialty clothing. In monopolistic competition, each firm holds a portion of the market due to brand differentiation and consumer preference.