The elasticity of demand refers to the degree to which demand will change concomitant to a change in another economics factor. The most common of these factors would be price. If the demand for a product changes inversely proportional to the change in price (as price increases, demand decreases) this would be considered ‘elastic demand’. However, with something like water, we will not see people drink less water if the price increases. This is ‘inelastic demand’. Elastic products almost always have substitutes, and if not, they are superfluous.