1. Abbr. cal Any of several approximately equal units of heat, each measured as the quantity of heat required to raise the temperature of 1 gram of water by 1C from a standard initial temperature, especially from 3.98C, 14.5C, or 19.5C, at 1 atmosphere pressure. Also called gram calorie, small calorie.
2. Abbr. cal The unit of heat equal to 1/100 the quantity of heat required to raise the temperature of 1 gram of water from 0 to 100C at 1 atmosphere pressure. Also called mean calorie.
3. a. Abbr. Cal The unit of heat equal to the amount of heat required to raise the temperature of 1 kilogram of water by 1C at 1 atmosphere pressure. Also called kilocalorie, kilogram calorie, large calorie. b. A unit of energy-producing potential equal to this amount of heat that is contained in food and released upon oxidation by the body. Also called nutritionist's calorie.