What Is Demand The official definition of demand is as such: Demand is the relationship between price and quantity demanded for a particular good and service in particular circumstances. For each price the demand relationship tells the quantity the buyers want to buy at that corresponding price. The quantity the buyers want to buy at a particular price is called the “Quantity Demanded.” So what determines the amount of a product that people are willing to buy? Demand refers to the willingness and ability of a person to purchase the good or service. Economists answer these questions by studying every factor in the decision a consumer ma