Thermodynamics is the branch of physics that studies energy, heat, and their transformations in physical systems. It is governed by four fundamental laws that describe energy conservation, entropy, and equilibrium. The key concepts include work, heat, internal energy, and entropy, which explain how systems exchange energy and move toward equilibrium. Thermodynamics has applications in engines, refrigeration, chemical reactions, and understanding natural processes. It bridges macroscopic observations with microscopic particle behavior, linking classical and statistical mechanics.