A liquid (or solid) with both viscous and elastic properties. A viscoelastic liquid will deform and flow under the influence of an applied shear stress, but when the stress is removed the liquid will slowly recover from some of the deformation.

having viscous as well as elastic properties

condition of a body that is both elastic (Hookean) and viscous (Newtonian)

Characterized by changing mechanical behavior, from nearly elastic at low temperature to plastic, like a viscous fluid, at high temperature.

Introduction | A. Shear flow