Energy in transit:

             The form of energy that is transferred from a hot body to a cold body is called heat. Thus, Heat is, therefore, called the energy in transit.

             Once heat enters a body, it becomes its internal energy and no longer exists as heat energy.

Internal energy:

                The sum of kinetic energy and potential energy associated with the atoms, molecules, and particles of a body is called its internal energy.

                The internal energy of a body depends on many factors such as the mass of the body, kinetic and potential energies of molecules, etc.