To me, the word 'Dom' is used to describe someone's preferred role in the lifestyle though I think Master or Mistress is a title that is earned. Then you've also got Tops as opposed to Dominants... as a submissive, I have tried to Top but I most certainly haven't been able to Dominate someone.

Let me describe it this way... when I play with someone, I'll call them whatever feels appropriate (hence the 'titles are earned' ) Usually when I play with someone new, I call them 'Sir' because that's my default, when I feel like I trust them enough or feel submissive enough to that person, maybe the title will change from 'Sir' to 'Master' ... it might be in one session or it might take several. It all depends on how I feel; if it feels right, then the word "Master' really slips out for me.