What is thermodynamics ?

Explanation

Thermodynamics is the branch of physics that deals with the concepts of heat and temperature and the inter-conversion of heat and other forms of energy.
OR
Thermodynamics is the branch of physics governing the transformation of heat and heat energy to and from other forms of energy its conditions and necessary machines.
Thermodynamics is a macroscopic science deals with bulk systems and does not goes into the molecular constitution of matter.
Thermodynamics description involves relatively few macroscopic variable of the system which can be usually measured directly. For example, for microscopic description of a gas would involve specifying the coordinates and velocities of the numbers of molecules of the gas.
By thermodynamics macroscopic quantities of gas like pressure, volume, temperature, mass and composition can be measurable.