I read something recently from Brian Wampler of Wampler effects who stated that the difference between distortion and overdrive is that distortion dumps a portion of the signal to ground from the opamp feedback loop, and overdrive doesn’t - distortion also has a high pass filter before the clipping diodes.
Fuzz is a more extreme form of muck, where the signal goes through cascading gain stages, rather like running 3 or 4 distortion pedals in your signal path.
I’ll see if I can find the link.