Demand is defined as the quantity of a commodity that consumers are willing and able to purchase at a given price in a given time period. Demand can be categorized based on the nature of the commodity, time period, and relationship to other goods. Law of demand states that, all else equal, demand is inversely related to price - as price increases, demand decreases, and vice versa. Factors that influence demand include price, tastes, income, prices of substitutes and complements, and expectations about future prices and income. Elasticity refers to the responsiveness of demand or supply to price changes. Income elasticity measures the responsiveness of demand to changes in income. Cross-price elasticity measures the responsiveness of demand