This document discusses the concept of elasticity of demand. It defines elasticity as measuring the change in quantity demanded relative to price changes. Demand can be elastic, meaning quantity demanded changes a lot as price changes. Demand can also be inelastic, where quantity demanded changes little as price changes. Price elasticity of demand is a measurement of consumption change relative to price change, and can be elastic, inelastic, or unitary elastic depending on if the measurement is greater than, less than, or equal to one, respectively.