When my hubby and I were first talking about what would be allowed (it was our first foray into poly afterall) we actually spent time describing and coming to a consensus about how WE were to define physical acts. Everyone has different ideas as to what constitutes what, even for the most basic terms. I had a boyfriend who thought "making out" was having sex!
As I was the one with an interest in someone else, I let my husband tell me what he was comfortable with at the time and then if I had questions or felt he left anything out, I just asked him, "well what about this?" As time went on, the boundary changed until he was comfortable with the idea of my having sexual intercourse with this other person...probably should have a chat with him again to see if this was just with Elric or with any gent I happen to develop a relationship with.
It's all about communication. Sometimes it's easy once you get started talking about it. Whatever you do, do not worry about "fine tuning" everything. Just a good general or semi-specific definition that you both can agree upon is great.
Life is about the journey and not the destination,
so what better way to know life
than to wander all the roads and paths set before you.