Marginal demand is the term in economics that refers to 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, marginal demand falls. And conversely, as prices for goods or services fall, marginal demand rises.
A product or service where price changes cause a relatively big change in marginal demand is said to have an elastic market. A product or service where price changes cause a relatively small change in marginal demand are said to have an inelastic market.