Trainer question?

How are the dynamics different between a Trainer and Dom/me?
I think that I am starting to understand the dynamics of a Dom/me, Master, And top but now I'm confused as to where the Trainer comes in? Is it because their sole purpose is to specifically train?

I met a man the other day that called himself The Trainer that had some very interesting views that has left me a little confused.
I was told that the role of the Trainer is not the same as other dominant roles and that a Trainer is not a Dom but is very Dominant.
I understand the concepts of Trainer/student in a teaching setting but am having a little trouble understanding how, if I am to submit, does that make it different then a Dom/me, Master, Top?