Absolute zero is the term used for the lowest temperature possible.
When the USS Enterprise first scanned the insectoid ship it encountered in 2270, it appeared to have a temperature of absolute zero, an impossibility. Later, it was discovered that the insectoid ship's energy accumulating wands, which collected many types of energy, were causing the sensors to return false data. The heat was being absorbed by the wands, leaving none to be detected. (TAS: "Beyond the Farthest Star")