Private Messages (also known as personal messages or PMs for short) are a feature on totaljerkface.com. Private messages are used as a way to communicate with other members of Total Jerkface privately, as they can not be seen by others, as suggested by their name. When a user is logged in, they can see how many new messages they have in the top-right corner of the Home Page, in between their username and the logout feature.
There is a quite common bug present for some users that will say they have messages (the number will vary), though their inbox is in fact empty. This will be stuck here for very long intervals of time, if not forever, and will always say they have that many messages. This has already been fixed. Jason has said that this will be fixed with the "site architecture" update, which will presumably include new forums and a new message system.
Due to very frequent glitches, and using a lot of server bandwidth, the message system has been shut down. It is unknown when (or if) it will be replaced.