This is the command you use in the Chatterbox to send a private message to another monk. The full form is
/msg RecipientName Text of message...You can enter such a command in any text box where, if you typed any other text, it would go to the public Chatterbox.
Note that this command is parsed on the first and second whitespace. This can cause a problem if the RecipientName contains any spaces. To get around this, you can enclose the recipient monk's name in square brackets. This syntax should be familiar, because it's how you create a link to a monk's homenode. Example:
/msg [Mr. Muskrat] Check out that new obfu!Further info is available in Using the Chatterbox: Private Messaging.
Also see the Message Outbox.