PM

From OLSEncyclopedia

Private Message, or PM for short, is a term used to describe a special type of post that is only seen by a select few members of the forum. The person who sends this private message can specify the recipient(s) of the message. This is useful for a number of things where posting a thread, even in the general discussion area of the message board, would be too much.

PMs should be used whenever possible for communicating to specific members of the forums, unless a public post (or even starting a new thread) is truly necessary.