Tone and related terminology (?)

Looks like there are many definitions then. I'm using these:

[Distortion, noun]
A distortion is the (usually) undesirable alteration of the original shape (or other characteristic) of an object, image, sound, waveform or other form of information or representation. Distortion is sometimes denoted as the amount of difference between the entity's original shape and its altered shape and can be quantified as a percentage of the magnitude of the original entity.

[Overdrive, verb]
The practice of forcing output of a guitar amplifier past maximum, resulting in distortion

http://encyclopedia.thefreedictionary.com/

By the way, IIRC you have a professional background in stuff like this, so I'm not doubting the correctness of your statement in any way.

Overdrive is a waveform that is mishapen, but still within the bounds of headroom (the wavetop is still a curve). Distortion is where the waveform exceeds the available headroom and causes clipping of the wave tops (the're flat) - increasing amplitude further leads eventually to a square wave (i.e. fuzz).
I've always thought that (not sure where I learned it from). The confusion comes from the fact that 'misshapen' and 'distorted' are synonyms. An overdriven signal is distorted literally but it's not distortion in this context. (Arjen, put the dictionary away! :mrgreen:)

Anyhoooo, people who know the difference are rare enough that I find you can use the terms interchangable - you should certainly be expecting others to do so if you want to avoid confusion.

Some sound clips might help. Here is an example of overdrive, Alright Now by the group Free, one of my favorite all-time rockers.

http://www.youtube.com/watch?v=fCN1BJkuoMk

Now, overdrive is a distortion, but it is a less heavy distortion. It has milder breakup. I would also call this guitar tone very "tight", you can really hear the individual strings, it is not a muddy sound. There is both good bass (low end) and highs in this song. I would absolutely call this a great example of "crunch". AC/DC gets great crunch tones in many of their songs as well. It is tight and focused sounding.

And not to change the subject, but Paul Kossoff of Free had the greatest vibrato EVER. Check out his solo. :D

Now, here is an example of "distortion"

http://www.youtube.com/watch?v=2RjL5Yh6qWo

The Smashing Pumpkins often used massive distortion as in this song. You will notice it is not quite as "tight" or focused sounding as the earlier song. Heavy distortion is fuzzy and often sounds like static. This is a pretty good example of "fuzz" tone.

Going back, here is another good example of overdrive. This is Cocaine by Eric Clapton. This is your classic Blues player type overdrive. It is often obtained without a pedal, but by simply cranking a tube amp into saturation. The tubes will naturally start to overdrive or distort. This is a very mild, but great sounding type distortion.

http://www.youtube.com/watch?v=Fnn1dDVmZyQ

I would also call this a tight, focused overdrive.

Hope this helped.