A chemical process in which a substance reacts with oxygen and give off heat is known as combustion. The substance that undergoes combustion is called as combustible or fuel. During the combustion, light is also given off either in the form of a flame or as a glow. The fundamental difference is that combustion is heating and no flames are created because much of the energy is converted to light energy in burning, resulting in less heat energy compared to combustion. If a flame is made in a combustion process, it is referred to as burning.