This document discusses price elasticity of demand (PED). PED measures how responsive quantity demanded is to a change in price. It defines goods as elastic, inelastic, or perfectly elastic/inelastic. Elastic goods have a PED greater than 1, meaning quantity demanded responds more than proportionally to price changes. Inelastic goods have a PED less than 1, so quantity demanded is less responsive to price. Perfectly elastic/inelastic goods have a PED of infinity/zero, where quantity demanded is completely responsive/unresponsive to price changes. The document provides examples of demand curves for different types of goods to illustrate how their quantities respond to price.