absolute zero

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The theoretical temperature at which substances possess no thermal energy, equal to 0 K, −273.15°C, or −459.67°F.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun slang A person or thing of absolutely no consequence.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun (cryogenics) the lowest temperature theoretically attainable (at which the kinetic energy of atoms and molecules is minimal); 0 Kelvin or -273.15 centigrade or -459.67 Fahrenheit