Definition of Absolute Zero from Wikipedia: > Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperatu

Definition of Absolute Zero from Wikipedia: > Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all thermal motion ceases in the classical description of thermodynamics. > Absolute zero is the lower limit of the thermodynamic temperature scale, a state at which the enthalpy and entropy of a cooled ideal gas reaches its minimum value, taken as 0. > In the quantum-mechanical description, matter (solid) at absolute zero is in its ground state, the point of lowest internal energy. It's still possible to squeeze some energy from a system past Absolute Zero as defined using Casimir effect, so it's possible to reach temperature below 0K. I know, that current interpretation of negative temperatures at Kelvin scale is different, but definition of temperature is different in that interpretation too, so let ignore it.