I think the word explains it...
it is a powerful shock-wave that goes through the combustion chamber when conditions are not idea (preignition, to lean, too hot etc)
This shock-wave can begin in several different ways
-hot spots on the piston dome and head can cause the fresh charge to pre-ignite it multiple locations simultaneously, causing a sudden impulse, can be caused by being too lean, too hot, or simply poorly designed (sharp angles/edges)
-as per the above but caused by a high concentration of hot exhaust gases re-entering the combustion chamber, acting like a million tiny embers. this effect was harnessed by Honda on the CRM250AR to perform controlled detonation to achieve a cleaner 2T combustion.
-the flame front travels too far if the motors squishband is wrong causing it to build up mommentum as it moves accross the full bore length? confirm the definition of this one
- I believe also that extreme pressures can cause the mixture to self ignite also, technically I believe this is referred to as detonation also (high compression diesel trucks?)
-two stroke piston rattle is a mechanical rattling sound whereas detonation is a pinging sound (why its called pinging)
the pinging sound is the detonation/explosion occurring over a very short time span. Honda worked out in the 90s how to measure this shockwave pinging. They installed detonation sensors, a ring that went under the spark plug that transmitted some form of electrical pulse every time it detected a violent explosion.
by measuring the level of pinging they could determine the perfect bike tune up (a certain number of detonations per second indicates a perfect tunup for making HP but not enough detonations to cause damage.)