critical temperature, T c

https://dx.doi.org/10.1351/goldbook.C01402
That temperature, characteristic of each gas, above which it is not possible to liquefy a given gas.
Source:
PAC, 1990, 62, 2167 (Glossary of atmospheric chemistry terms (Recommendations 1990)) on page 2183
PAC, 1993, 65, 2397 (Nomenclature for supercritical fluid chromatography and extraction (IUPAC Recommendations 1993)) on page 2399