Deflagration

Deflagration (Lat: de + flagrare, "to burn down") is a term describing subsonic combustion propagating through heat transfer; hot burning material heats the next layer of cold material and ignites it. Most "fire" found in daily life, from flames to explosions, is deflagration. Deflagration is different from detonation, which propagates supersonically through shock waves. This means that when a substance deflagrates, it burns extremely quickly instead of exploding. Black powder is an example of a substance that deflagrates; when it is ignited, black powder burns extremely fast (so fast in fact that the burn is sometimes mistaken for an explosion).