Re: Fuzz vs. Distortion
Generally speaking, overdrives employ soft clipping (which means those parts of the sine waves that exceed the clipping point get squashed), while distortion employs hard clipping (which means those parts get cut off). Fuzz pedals vary a lot, but generally they are function like distortion pedals that amplify a lot and clip aggressively, resulting in a heavily clipped sine wave (looking more like a square wave). The very "sharp" edges of the clipped wave are what makes it sound buzzy.
It is complicated a bit because many overdrive pedals can act like distortion pedals when cranked hard enough (or fed a signal of high enough amplitude), and similarly, many distortion pedals can act like fuzzes when cranked hard enough or fed a high amplitude signal.
Because of that, the categories are to a large extent a matter of degree rather than of kind, and so there are no real hard-and-fast rules to what overdrive is, what distortion is, and what fuzz is. It doesn't help that some pedals do things like asymmetrical clipping, with half of the wave being hard-clipped and half being soft-clipped; or using different components (germanium vs. silicon transistors, etc) to alter the sound in various ways.
My rule is simple, though... It's down to the ear of the beholder. If it sounds round and smooth it's overdrive, if it's harsher and more aggressive it's distortion, and if it's fuzzy and buzzy it's fuzz.