Internal energy.
Explanation:
In any substance/object, the particles inside it (atoms/molecules) constantly move in random directions and with random speeds (this motion is called Brownian motion). As a result, the particles have some kinetic energy (which is proportional to the temperature of the substance). Moreover, the particles interact with each other due to the presence of electrostatic intermolecular forces, and as a result, the particles also have some potential energy.
The sum of the kinetic energies and potential energies of the particles in a substance is called internal energy.
