Marginal demand
Marginal demand  in economics is the change in demand for a product or service in response to a specific change in its price.

Normally, as prices for goods or service rise, demand falls, and conversely, as prices for goods or services fall, demand rises.

A product or service where price changes cause a relatively big change in demand is said to have elastic demand. A product or service where price changes cause a relatively small change in demand is said to have  inelastic demand. See Elasticity of demand.