Elasticity in physics refers to the ability of a material to return to its original shape after being deformed by an external force. When a force is applied, materials can stretch, compress, or bend, but if they are elastic, they will revert to their initial form once the force is removed. This property is crucial in various applications, from rubber bands to springs. The degree of elasticity is often measured by the Young's modulus, which quantifies how much a material will deform under stress. Different materials exhibit different levels of elasticity; for example, rubber is highly elastic, while glass is brittle and breaks rather than deforms.