Elasticity of demand

The tern elasticity denotes the quantity of a good that can expand and contract.Hence,the change in quality demanded due to change in price is called elasticity of demand.The concept of elasticity of demand was introduced in economics by economists like Cournot,J.S.Mill.The credit is given to Dr.Alfred Marshall for the development of the concept.
The law of demand tells that the quantity demanded of a commodity varies investment with price.But it does not tell how much quantity demanded change with change in price.This task is accomplished by quantity demand change with in change price.
In the words of Alfred Marshall -"The elasticity of demand is a market is great or small as the amount demanded increase much or little for a given fall price and diminished much or little for a given rise in price."
According to Stonier and Hague -"Elasticity of demand is,therefor,a technical term used by the economists of describe the degree of responsiveness of the demand for the commodity to a fall in its price."
In brief,elasticity of demand measures the rate of change in quality demanded as a result of the change in price.