Heat

1. In thermodynamics, heat is energy in transfer to or from a thermodynamic system, by mechanisms other than thermodynamic work or transfer of matter (e.g. conduction, radiation, and friction).
2. Heat is the transfer of kinetic energy from one medium or object to another, or from an energy source to a medium or object.

Heat is what scientists call the form of energy that is transferred between two materials of different temperature. This transfer of energy occurs because of differences in the average translational kinetic energy per molecule in the two materials. Heat flows from the material with higher temperature to the material with lower temperature until thermal equilibrium is reached. The SI unit of heat is the joule, where 1 joule = 1 newton × meter.

Sources:

Vedantu: Learn Live Online https://www.vedantu.com/physics/

Thermodynamics and an Introduction to Thermostatics, 2nd Edition, by Herbert B. Callen, 1985, http://cvika.grimoar.cz/callen/

Heat https://sciencing.com/heat-physics-definition-formula-examples-13722754.html