What is it called when molecular motion stops?

Absolute zero is the theoretical temperature at which all atomic motion stops. However, this temperature is unattainable, because it represents a complete lack of energy within particles of matter. Even in deep space, this temperature cannot be reached so, like the speed of light, it is a scientific limit which can only be approached. On the Kelvin scale it's 0, on the Celsius scale it's -273.16.