Answer: Elasticity is an economic concept used to measure the change in the aggregate quantity demanded of a good or service in relation to price movements of that good or service.
Explanation: A product is considered to be elastic if the quantity demand of the product changes more than proportionally when its price increases or decreases. Conversely, a product is considered to be inelastic if the quantity demand of the product changes very little when its price fluctuates.
For example, insulin is a product that is highly inelastic. For people with diabetes who need insulin, the demand is so great that price increases have very little effect on the quantity demanded. Price decreases also do not affect the quantity demanded; most of those who need insulin isn't holding out for a lower price and are already making purchases.
On the other side of the equation are highly elastic products. Spa days, for example, are highly elastic in that they aren't necessarily good, and an increase in the price of trips to the spa will lead to a greater proportion decline in the demand for such services. Conversely, a decrease in the price will lead to a greater than proportional increase in demand for spa treatments.