Demand is the quantity of a product or service that consumers are willing and able to buy at a certain price over a given period. The law of demand states that as the price of a product increases, the quantity demanded of that product decreases, and vice versa. Supply refers to the quantity of a product or service that producers are willing and able to sell at a certain price over a given period. The law of supply states that as the price of a product increases, the quantity supplied of that product also increases, and vice versa. The five factors that cause demand and supply curves to shift are changes in consumer income, prices of related goods, tastes and preferences, demographic factors, and consumer expectations for demand, and changes in production costs, technology, prices of related goods, natural conditions, and government policies for supply. Equilibrium occurs when the quantity demanded of a product equals the quantity supplied, resulting in a stable market price. In a market economy, price serves as a signal to both buyers and sellers of the relative scarcity or abundance of a product and the level of demand for it, which helps allocate resources efficiently. The elasticity of demand refers to the degree to which the quantity demanded of a product changes in response to a change in the product's price.