Send a private message to another player.
/pm name message
name is the username you want to send the message to. It can be the whole name or enogh to identify the user.
message is the message you want to send.
In both cases you may need to put quotes (") around the name and/or message if they have any spaces in them.
eg
/pm madone "How are you today ?"
The message will only be visible on the player that you name and nobody else will see it. The name does not need to be on your team.
This would be an ideal way to pass a message to an admin without making it visible to others.
eg
/pm smithy "item x seems to be broken"
See Admins for a current list of admins.