Levels in D/s for me...

First off... Sex, love and BDSM are 3 totally different things for me, and I hardly ever mix them together, but there always exceptions!

Friends or newbie : Someone I will do a service for or just friends with.
Playmates: someone I play with at least semi-regularly
Sub(missive): someone I play with who is submissive to me.
Slave: a sub I have taken in and own.

Top/Bottom - Physical positions. Literally a person on top or bottom of an action.
Dom(inat)/sub(missive) - mental positions. Where is your headspace when playing?
Master/slave - Titles. You can only be a master or slave if owned or own someone. Also master can be a term used for high skill level at your choice of D/s style or preferred activity. And I expect people who use "master" as a skill level to prove that they are at that level!
Switch - someone which plays or changes roles between scenes such as... dom/bottom, top/sub, dom/sub or top/bottom.
Mega-slut - a bi-poly-switch which is common to see in TNG's
22's - my code word for a pro-dom.