This is a common question and frankly I am not sure if there even is a question. You are what you feel you are, whatever the name given to that state by the lifestyle.

If we are dealing with strict definitions then I would say that a submissive is a person who submits to a Dominant - whether that be for one session or forever, whether they be a switch or always a sub and regardless of the Dominant involved. A slave, on the other hand, is ALWAYS submissive to a particular dominant as they are THEIR slave but may be a sub to others if their Dom allows.

However, there are many different definitions of the above terms and there are bound to be some who disagree mine...

Subordinate is something I would more associate with a Dom/me in training - someone who works with a Dom/me on another sub, performing some of the Dominant functions of the relationship. i.e. someone who does the work of tying someone up while the real Domme 'supervises' from a comfy seat. In this case, both are subs because they are taking orders from the Dom/me but one of them is also acting as a Dom/me themselves and may one day be a Dom/me in their own right.