Combustion is the process of burning a substance in the presence of oxygen, producing light and heat. It involves exothermic chemical reactions between a fuel and an oxidant. Burning produces light and heat. LPG is useful for cooking. Combustible substances burn to produce light and heat, while non-combustible substances do not. Spontaneous combustion occurs without an ignition source through heat buildup during oxidation. Rapid combustion releases a lot of heat and light quickly, and sometimes gas.