The chemical decomposition (burning) of a material in which the reaction front advances into the reacted material at less than sonic velocity.

Very rapid combustion sometimes accompanied by flame, parks or spattering of burning particles. Deflagration, although classed as an explosion, generally implies the burning of a substance with self-contained oxygen so that the reaction zone advances into the unreacted material at less than the velocity of sound in the material.

In this case, heat is transferred from the reacted to the unreacted material by conduction and convection. Burning rate usually less than 2,000 meters/second.