It stands for "private message". It is a communication tool and, I would think, a valuable resource in your attempts to secure clients.
So tell me why it is, that so many providers FAIL to respond to messages on a timely basis, if at all? It seems to me that correspondence on this site would be preferable to less secure media like texts or emails. Is there some reason that the ladies are hesitant to use pm's? Is it less convenient or too hard to use?. Does it ever occur to you that poor communication could be costing you business?