elasticity

Elasticity is important because it describes the fundamental relationship between the price of a good and the demand for that good.

Elastic goods and services generally have plenty of substitutes. As an elastic service/good's price increases, the quantity demanded of that good can drop fast. Example of elastic goods and services include furniture, motor vehicles, instrument engineering products, professional services, and transportation services.

Inelastic goods have fewer substitutes and price change doesn't affect quantity demanded as much. Some inelastic goods include gas, electricity, water, drinks, clothing, tobacco, food, and oil.

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To learn more about specific types of elasticity, see the following:

Income Elasticity of Demand: the responsiveness of quantity demanded to a change in income.
Price Elasticity of Demand (PED): the responsiveness of quantity demanded to a change in  price.
Elasticity of Supply: the responsiveness of the quantity supplied to a change in price.