the greeter is an earned title for any player that voluntarily helps new players/exhisting players. the target player is like a community ambassidor - but no ingame powers are to be bestowed. the greeter, essentially helps the playerbase, example "RoyalSerf".
The player I have named is a universally accepted "friend to everyone" and quite a knowledgeable player. I think everyone knows who she is, and no finer example of selfless behaviour could be chosen, for who gets "first" greeter status.