An explosion is a rapid increase in volume and release of energy in an extreme manner, usually with the generation of high temperatures and the release of gases. An explosion creates a shock wave. If the shock wave is a supersonic detonation, then the source of the blast is called a “high explosive”. Subsonic shock waves are created by low explosives through the slower burning process known as deflagration.
Reference: Lees’ Loss Prevention in the Process Industries
Explosion is a release of energy sufficient to cause a pressure wave.
Reference: S2S (safety to safety website: HarsNet working group, 2002, HarsBook, A technical guide for the assessment of highly reactive chemical systems, Frankfurt.)