Detonation is when fuel explodes hardcore instead of burning, I have a nice fun video somewhere of a badly tuned/bad running VL turbo doing a nice impression of detonation about 3 seconds before it chucked half the motor out onto the track
. WrrrrreEAAAAAAputAputAAAAAAH put put BANG BANG BANG put BANG crunch, dead. Something like that.
pre ignition is just when it catches fire before it should have, from the timing being wrong or a overheated motor/carbons all that stuff they are both the same kinda thing in that one can cause the other but detonation is a whole lot more serious than a little ping here and there because it will kill the motor and really fast