The lowest possible temperature, attained when a system is at its minimum possible energy. The Kelvin temperature scale sets its zero point at absolute zero (-273.15 on the Celsius scale, and -459.67 on the Fahrenheit scale).
The idea of a true minimum temperature has been confirmed by many experiments. Given the concept of temperature as molecular energy it follows that there must be a point at which no further energy can be extracted from a system.
Although it is possible to approach ever closer to absolute zero, the “third law” of thermodynamics holds that it is impossible to attain absolute zero in a system.
The present temperature of the cosmic background radiation is about 2.7 degrees above absolute zero. If the universe expands forever, this temperature will asymptotically approach absolute zero.