Final answer:
Test marketing is the promotion and sale of a product in a limited area to assess consumer reaction and sales. In monopolistic competition, advertising differentiates products and can alter a product's perceived demand curve, affecting sales and prices.
Step-by-step explanation:
When a new product is promoted and sold in a limited geographical area to gauge consumer reaction and sales figures, this practice is known as test marketing. Test marketing allows a company to gather data and understand how their product performs before a full-scale launch. In the context of monopolistic competition, advertising plays a critical role in differentiating a product from its competitors, which can make the demand curve either more inelastic or shift it to the right, resulting in potentially higher sales or prices.