Zero-point energy is the lowest possible energy which a quantum mechanical physical system may have; it's the energy of its ground state. All quantum mechanical systems have variations even in their ground state and still have a related zero-point energy, due to the Heisenberg uncertainty rule.
Due to the uncertainty theory all physical systems, even at absolute zero temperature, contain a zero-point energy that is more than zero. Liquid helium-4 (4He) continues to be liquid-it does not freeze-under atmospheric pressure no matter how low its temperature is, due to its zero-point energy.
zero-point energy originated in Germany by a group of physicists, amongst them Max Planck (1911), Albert Einstein and Otto Stern (1913). In 1916 Walther Nernst postulated the fact that vacuum of space is filled with zero-point electromagnetic radiation. The definition of zero-point energy comes from the German Nullpunktenergie.
Vacuum energy is the zero-point energy of all of the fields in space, which in the Standard Model contains the electromagnetic field, other gauge fields, fermionic fields, as well as the Higgs field. It's the energy from the vacuum, which in quantum field theory is defined not as empty space but as the ground state of the fields. In cosmology, the vacuum energy is but one possible explanation for the cosmological constant. The deviation in zero-point energy as the boundaries of a region of vacuum shift leads to the Casimir effect, which is visible in nanoscale devices. A related term is zero-point field, that is the lowest energy state of a particular field.