An economic shortage is a disparity between the amount demanded for a product or service and the amount supplied in a market. Specifically, a shortage occurs when there is excess demand; therefore, it is the opposite of a surplus.Economic shortages are related to price—when the price of an item is set below the equilibrium rate determined by supply and demand, there will be a shortage. In most cases, a shortage will compel firms to increase the price of a product until it reaches market equilibrium. Sometimes, however, external forces cause more permanent shortages—in other words, there is something preventing prices from rising or otherwise keeping supply and demand balanced.In common use, the term "shortage" may refer to a situation where most people are unable to find a desired good at an affordable price. In the economic use of "shortage", however, the affordability of a good for the majority of people is not an issue: If people wish to have a certain good but cannot afford to pay the market price, their wish is not counted as part of the quantity demanded at that price.