Celsius temperature, t, θ

Thermodynamic temperature minus 273.15 K, invariably expressed in the SI unit degree Celsius(°C) which is equal to the kelvin. Sometimes the misnomer centigrade temperature is used for Celsius temperature.
Green Book, 2nd ed., p. 48
PAC, 1996, 68, 957 (Glossary of terms in quantities and units in Clinical Chemistry (IUPAC-IFCC Recommendations 1996)) on page 965