The term "pm me" is a common Internet expression, frequently found on forums, which means, "Send me a private message." It is a way for members of the same platform to communicate privately with each other. Messages exchanged via PM are only accessible to the users involved in the message.
There are two distinct types of private messaging: a feature that is part of a larger social networking site and direct communication on its own platform. Examples of private messaging as a feature on a social networking site include Twitter's direct messages and the Facebook Inbox. Kik and Whatsapp are both dedicated private messaging platforms that allow users to maintain privacy during conversations. Private messaging is sometimes called personal messaging or direct messaging.