This document discusses the concept of elasticity in economics. It defines elasticity as measuring how changing one economic variable affects others, such as how much more a product will sell if the price is lowered or how much less it will sell if the price is raised. It provides mathematical definitions for elasticity and discusses several specific types of elasticities, including price elasticity of demand, income elasticity of demand, cross elasticity of demand between firms, and elasticity of supply. It explains how these different elasticities capture the responsiveness of economic variables, such as quantity demanded or supplied, to changes in factors like price, income, or other prices.