I have been wondering this for a while... you too?
Answer: '
OP' has two common meanings in the 21st century. It will sometimes mean 'overpowered' in the world of online gaming. More commonly,
OP means 'original poster' in discussion forums. The original poster is the person who started a discussion thread, and OP is used to refer back to that person as the responses grow.
Found it here:
http://netforbeginners.about.com/od/internetlanguage/f/What-Is-OP.htm