Real Dictionary

explosion
countable noun: An explosion is a sudden, violent burst of energy, for example one caused by a bomb.
variable noun: An explosion is the act of deliberately causing a bomb or similar device to explode.

explosion in American English
an exploding; esp., a blowing up, or bursting with a loud noise; detonation
noun: an act or instance of exploding; a violent expansion or bursting with noise, as of gunpowder or a boiler (opposed to implosion)

explosion in Automotive Engineering
noun: An explosion is a very rapid combustion, with a sudden loud noise, that is damaging to internal combustion engines.

explosion in British English
noun: the act or an instance of exploding

explosion in Chemical Engineering
An explosion happens when a free gas expands very quickly, because of a chemical reaction that produces a gas, or because a container of pressurized gas ruptures.