As stated in Post # 2, it is called "Price Elasticity of Demand" when consumers purchase less of a product if the price increases. The price elasticity of demand, using a mathematical formula, gives an exact calculation of the effect of a change in price on the quantity that consumers demand.
Economists use this calculation to understand how consumers will react to price increases. This helps them formulate conclusions on how the economy in a nation, or region of a nation, will handle price fluctuations, based on consumer behavior. They measure the sensitivity of demand as relates to consumers' attitudes to increased prices and the actions they take (buying or not buying) because of price changes.