Heat is the transfer of energy generated by a temperature gradient. Heat is generally measured in joules, though calories and BTUs are also used as units.
Heat Attribute in Ayurvedic Medicine and Traditional Chinese Medicine
In Ayurvedic medicine heat/hot is one of the 20 attributes. Heat is the attribute of pitta dosha and also of agni. It is the opposite of cold-cool or vata, kapha and ama.