A unit of measurement named after British scientist, William Thomson, Lord Kelvin (1824 - 1907). One Kelvin degree is equivalent to one Celsius degree. The difference between the two temperature scales: All motion within an atom ceases at zero Kelvin (K) -- this point is called absolute zero. Water freezes at zero degrees Celsius, which is approximately 273.16 Kelvin. [ K = C + 273.16]