What is "quantum solid"

n. (context physics English) any of a class of solids (such as that of helium) whose atoms or molecules undergo large zero-point motion even in the quantum ground state (at absolute zero)

In physics, a quantum solid is a type of solid that is "intrinsically restless", in the sense that atoms continuously vibrate about their position and exchange places even at the absolute zero of temperature. The archetypal quantum solid is low density solid helium.