Final answer:
'K' is the abbreviation for Kelvin, a base unit of measurement for temperature in the International System of Units.
Step-by-step explanation:
'K' is the abbreviation for Kelvin, which is the base unit of temperature in the International System of Units (SI). The Kelvin scale is an absolute temperature scale where zero Kelvin (0 K) is the point at which all thermal motion ceases in the classical description of thermodynamics. In physics, the Kelvin is defined by taking the fixed numerical value of the Boltzmann constant k to be 1.380649×10-23 when expressed in the unit kg.m²-s¯²·K¯¹. Therefore, a temperature of 2900 K would be the thermal environment for a tungsten light bulb filament when in use.