Elasticity means responsiveness of one variable to change in another. It shows the degree of a change in a variable due to the change in quantity of another variable. Types include; Price, Income and Cross Elasticity of Demand.
Demand is the amount or quatity of particular economic goods or services that a consumers are willing and are able to purchase at a particular price for a period of time.
Economics is a branch of Social Science that deals with production, distribution and consuption of goods and services. It tends to the management of scarce resources(Land, Labour, Capital )