In physics & chemistry, thermodynamics (from the Greek θέρμη therme, meaning "heat" and δύναμις, dynamis, meaning "power") is the study of energy conversion between heat and mechanical work, and subsequently the macroscopic variables such as temperature, volume and pressure. Its progenitor, based on statistical predictions of the collective motion of particles from their microscopic behavior, is the field of statistical thermodynamics (or statistical mechanics), a branch of statistical physics.

Source: Wikipedia.org