This sounds like a question one would hear in philosophy class.
Hey, you can't have a forum for exercise technique without knowing what it means for technique to be proper, can you?
Plus I don't think this question will be as difficult to solve as other philosophy questions.
Now that I think about it more, I think we need to add 3) Work the desired muscle groups according to 4) the intended force/velocity relationship.
I'm glad you added "defined range of motion" into your definition, because I was expecting someone to say that the exercise has to go through a full range of motion. That obviously can't be right because there reasons for dong partials.