Technically, overdrive distorts the signal as well, otherwise it would be clean. Then again, EQ and compression distort the waveform as well. I think in common usage, overdrive and distortion are terms that describe different degrees of clipping type of distortion, and of course different ways of getting there. It's certainly open to interpretation as far as what each person calls it. A lot of times, people use overdrive as the word for pushing the AMP into distortion, and use distortion as the word for something that clips in front of a clean amp. To me, it's all the same thing, I just use 'distortion' to describe hard clipping, whether it comes from the amp or somewhere else.

Atomic

PS, it's been a Loooooong time since I've been here. Nice to be back. Check out the amps I build over at www.brimstoneamps.com