Distortion vs. Overdrive?

I've never been able to figure this out. What's the difference?
I'd like both a technical explanation and a qualitative description of how they are supposed to sound. Thanks.

Overdrive is the sound of output tubes 'clipping'. The sound compresses as to the fact that the power tubes takes all the power from the amp.

Distortion is overdriven preamp stages (tubes or transistors). Preamp stages don't need much power so the drive seems more 'powerful'

- Johnny

One thing I might add to our knowledgable posters, is that when it comes to effect pedals, I think you'll notice there are many different levels of both "overdrive" and "distortion". I've heard some overdrive pedals that don't do much more than give a slight harshness to the tone, but IMHO would still be considered clean. Where exactly a tone goes from heavy overdrive, to light distortion, is hard to say and probably a matter of opinion. There's also effect pedals out there for creating a "fuzz" sound. I really don't know if fuzz is something that can be produced analog or not. I believe it is supposed to be a signal that has been distorted beyond recognition.
Almost like chaining multiple distortion effects in series together.
Still other amps, like Line6 models, have a setting called "Insane".
I've also heard it called "crazy", "halucinagenic", and all sorts of other synonyms for for being over the top. This kind of effect will feedback on you with virtually every note. Chords have more definition to them than with a "fuzz" effect. This is often found usefull by death metal, thrash, or the occasional punk band. And there are definitely analog methods for recreating Line6's "insane" saturation.

Now, my confusion is with Blues driving. If that's even a real term.
Boss, DOD, Digitech, and many others have an effect pedal call "blues driver" or some variation of. Is this an overdrive EQ'd slightly differently? Never used one. Anyone know?