PM is short for private message.
Bump is usually associated with a message. If you haven't received a reply in a few days you might bump your message by adding something to it so that the latest date on it is updated. Bumping is usually frowned upon unless a few days have gone by.
Rather than bump a message, if the message is about a problem You can send a PM to a moderator asking for help since it has been several days.
You can put your mouse pointer over a user name a box will pop up, click on the button that says "Send a Message" to send a PM to that person.
You can find a moderator by following this link.
Edited by rotor123, 13 June 2013 - 07:25 PM.