Rapid combustion: It is a form of combustion in which large amounts of heat and light energy are released. Spontaneous combustion: It is a type of combustion which occurs by self-heating (increase in temperature due to exothermic internal reactions), followed by thermal runaway (self heating which rapidly accelerates to high temperatures) and finally, ignition.
Explosion - definition
An explosion is a rapid increase in volume and release of energy in an extreme manner, usually with the generation of high temperature and the release of gases. Eg., explosion during bomb blast and underwater nuclear test.