system
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human
What is the difference between combustion deflagration detonation and explosion?

Im very confused between these four terms. I've been researching fire and how it works and I ended up with these ones. From what I understand

Combustion is the process of fire.  
Deflagration is when fire travels slower than sound.   
Detonation and explosion are the ones that confuse me and is an explosion a type of combustion?
gpt
Flame front speed < speed of sound --> deflagration

Flame front speed > speed of sound --> detonation

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Combustion means fuel and oxidizer reacting. Sometimes the fuel and oxidizer are contained in the same molecule (for example: nitrocellulose), but more commonly they are separate molecules (for example: gasoline and oxygen). Combustion can result in fire, deflagration, or detonation.

Explosion is a term which means deflagration or detonation.  Other energy releasing reactions besides combustion could result in explosion, for example: a nuclear device going supercritical.

A flash fire is a deflagration.

It all comes down to pressure rise. If pressure is able to rise high enough then it results in detonation in which the flame front is traveling at supersonic speeds. This could be caused by a rapid reaction with a lot of energy released or by enclosing the reaction in a restricted volume (think hand grenade).