These are not specific to this forum. These abbreviations typically come from what is often called "text speak." It is simply a shorthand method that is used when typing text messages. It's used for convenience - to shorten what you have to write out. It has become pretty ubiquitous on online forums. There is a pretty exhaustive looking list of abbreviations used in texting and on forums here http://www.netlingo.com/acronyms.php.