A quantum fluid can refer to a cluster of valence electrons moving together after they undergo fermionic condensation

Fermionic condensate

A fermionic condensate is a superfluid phase formed by fermionic particles at low temperatures. It is closely related to the Bose–Einstein condensate, a superfluid phase formed by bosonic atoms under similar conditions. Unlike the Bose–Einstein condensates, fermionic condensates are formed using...

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Under extremely high pressures and low temperatures electrons may condense into a quantum fluid. In such a state, electrical current can theoretically flow forever with a complete absence of voltage

Voltage

Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...

, meaning that its electric potential does not change, as in a superconductor.(they are like a 5th state of matter)

Quantum fluids exhibit the remarkable property of remaining liquid at absolute zero temperature and zero pressure. This effect arises from their large zero-point energy

Zero-point energy

Zero-point energy is the lowest possible energy that a quantum mechanical physical system may have; it is the energy of its ground state. All quantum mechanical systems undergo fluctuations even in their ground state and have an associated zero-point energy, a consequence of their wave-like nature...

 and the small interatomic forces, both of which prevent the formation of a solid phase.

A quantum fluid can also refer to a superfluid

Superfluid

Superfluidity is a state of matter in which the matter behaves like a fluid without viscosity and with extremely high thermal conductivity. The substance, which appears to be a normal liquid, will flow without friction past any surface, which allows it to continue to circulate over obstructions and...

(made up of atoms).