Good question.

I don't have any definitions. I have simply trained the initial classifier with a selection of bots that I manually evaluated as such. In arriving at classifications for the initial training set, my biases towards what I consider to be a spam and bots will inevitably shine through. This will be reduced over time as the training data expands.

I'll answer with my current opinions anyway though, insofar is they relate to this project :)
If someone creates normal content, but votes using script - is he bot? Depends on proportions.
If someone only votes (manually, within small period of time) - is he bot? No.
If someone only makes witness actions - is he bot? No, it doesn't affect comments/posts.
If someone posts the same comment in response to specific posts - is he bot or spammer? Depends on whether it's scripted.

It is good to frame the project better though, and maybe I haven't given enough thought to that.