The kelvin (symbol: K) is a unit increment of temperature and is one of the seven SI base units. The Kelvin scale is a thermodynamic temperature scale where absolute zero ? the coldest possible temperature ? is zero kelvins (0 K).The Kelvin scale and the kelvin are named after the Northern Irish physicist and engineer William Thomson, 1st Baron Kelvin (1824 ? 1907), who wrote of the need for an ?absolute thermometric scale.? Definition of kelvin The