In the Celsius scale we use the temperature at which ice melts as the value zero. All lower temperatures are recorded as negative. Can the temperature reach any negative value?  Obviously not; when the particles which make up the body are at rest the body cannot get any colder.  At present we know that this state cannot be reached, but it serves to define the lowest temperature possible. 

We will call the temperature which corresponds to the lowest average kinetic energy of the particles in a body, absolute zero. 

Of the scales which use absolute temperatures the best known, recognized by the Système d'Unités International, is the Kelvin scale.

In the following visual we illustrate the correspondence between both scales by observing what happens to a gas as the temperature changes.