Definition from Wiktionary, the free dictionary
From French détonation.
detonation (plural detonations)
- An explosion or sudden report made by the near-instantaneous decomposition or combustion of unstable substances as, the detonation of gun cotton. Specifically, combustion that spreads supersonically via shock compression.
- Engine knocking, an improper combustion in internal combustion engines
Related terms 
- (with respect to speed of propagation): deflagration