Something with elasticity can be stretched or pulled and will return to its original size and shape. The elasticity of a balloon means that if you pop it, it shrinks back to the size it was before you blew it up.
Rubber bands have elasticity, and so do tennis balls and even human skin. The quality of something that stretches and then returns to its initial shape — its elasticity — is also a term in physics. Physicists describe it as the tendency of a solid object, after being deformed by forces applied to it, to return to its original shape when those forces are taken away. The Greek root of elasticity is elastos, or "flexible."