calorie

Non-SI unit of energy. There are three differently defined calories: thermochemical calorie ( $cal th = 4.184 J$ ), international steam table calorie ( $cal IT = 4.1868 J$ ), $15 °C$ calorie ( $cal 15 = 4.1855 J$ ), however only the symbol $cal$ is usually used.

Source:

Green Book, 2nd ed., p. 112

PAC, 1996, 68, 957 (Glossary of terms in quantities and units in Clinical Chemistry (IUPAC-IFCC Recommendations 1996)) on page 964