Thermal energy is the energy that comes from heat. It is the energy that comes from the movement of particles within a substance. The faster the particles move, the more thermal energy is produced.
Thermal energy can be produced in various ways, such as through friction, chemical reactions, or by adding heat to a substance. When you rub your hands together and they start to feel warm, that's the result of the production of thermal energy through friction.
Some common examples of thermal energy include: