No matter what, these molecules are moving around and are active. Moving atoms or molecules are called internal energy . An increase in internal energy results in a rise in temperature or a change in phase. We can then assume that if the temperature of matter has risen, there has been an increase in its internal energy. If its temperature has lowered, its internal energy has lowered as well.
Heat is likely to exchange between matter.
This process of exchanging heat is called heat transfer. Each is as important as the next. Conduction deals with the transfer of heat in matter in its solid state. Molecules then collide and heat it up when they pass objects. Heat can also be transferred within the same object.