The Kelvin is a unit of temperature. A change in temperature of 1 degree Kelvin is exactly the same as a change in temperature of 1 degree Celsius (Centigrade). Where Celsius and Kelvin differ is in their zero-points, i.e. zero degrees Celsius is defined as the freezing point of pure water, while zero degrees Kelvin is defined as the lowest physically achievable temperature – referred to as absolute zero. This corresponds to a total lack of thermal energy. Zero degrees Kelvin corresponds to a temperature of -273 degrees.