The thermal energy is that part of the energy which rises with the increase in temperature. It could be defined as a spontaneous transit in energy from one point to another. It is the result of the movement of molecules and atoms in the matter.
Few example of the thermal energy is when we rub our hand we do feel some kind of friction. Also, we feel the heat when we put our hand over the hot stove. Same is the case with molecules and heat. When they rub against each other they produce heat. Scientist has named that heat as thermal energy.