There are many words and sentences that tend to be abbreviated in posts. Most of the meanings to those abbreviations can be found here: http://www.ivillage.com/community/0,,nvmt,00.html

Some more commons ones that are not listed there are: LO (little one), IMHO (in my honest/humble opinion), KWIM (know what I mean), KUP (keep us posted), P & PT’s (prayers and positive thoughts).