Thermal energy is made by the movement of particles within an object or system. The thermal energy of an object, and thus the temperature of an object, increases as its molecules move more quickly.
In physics, we calculate thermal energy by combining what are known as the sensible and latent forms of internal energy within an object. Internal energy is a universal property for every object on Earth. It is equal to the sum of four potential aspects of internal energy: sensible energy, latent energy, chemical energy and nuclear energy. Sensible energy is associated with kinetic energy, while latent energy is associated with the phase of matter of the object: liquid, solid or gas. Thermal energy is the combination of the sensible and latent energies of an object.
To better understand thermal energy, Atoms for Peace gives the example of butter melting on a stove. The process of melting necessarily implies motion, or kinetic energy, and also necessarily implies latent energy via the process of changing from a solid to a liquid. The combination of these two energy processes is the thermal energy of the butter.
Thermal energy also applies to calories in food. In fact, it is possible to use thermal energy to calculate the caloric content of an item of food by measuring the thermal energy required to raise the temperature of one gram of the food by one degree.