It stands for Jun Fan Jeet Kune Do. Literally meaning "Bruce Lee's Way of the Intercepting Fist." Jun Fan being Bruce Lee's chinese given name and Jeet Kune Do (JKD) is a fighting concept invented by Lee. Well perhaps I shouldn't say "invented" because nothing new was actually formed in the development of JKD. Many people mistake Jeet Kune Do to be a new fighting style like Karate or Taekwondo or Judo when it's really not. Originally after Lee had transformed his knowledge into JKD, he wished he never had a name for it. Since Jeet Kune Do has no style, it can fit in with all styles. And since it has no way either, all ways are possible with JKD. A simple, direct attack was what Lee was aiming for in combat situations. He always emphasized the importance of simplicity and that complex combinations of attacks should, in most cases, be avoided. Be formless, he would say, like water, for if you put water in a cup it becomes a cup; in a bowl, a bowl; in a pool, a pool. And so on...
Gurl: U kno Kenny, he's a 1st Dan in TKD
Gurl: can u beat him up?
Guy: np, JFJKD owns all