A style of depicting fight scenes in movies, originating roughly around the turn of the 21st century. It contains one or more of the following traits:
1) Dark scenery contrasted by incomplete lighting (often with a feel such as "rave" or "industrial", augmented by appropriate music)
2) Increased footage speed
3) Inclusion of Matrix-style bullet time
4) Rampant movement of the camera, both in terms of erratic movement as well as frequent changes of shot entirely, creating an intentionally jarring viewing experience
Blur fu is often incorporated to make a movie appear edgy, hardcore, or to match other similar movies. It is also a tool to mask the fact that the performers onscreen may not be able to perform any real fight stunts worth watching.
Examples of blur fu can be seen in films like Alien Vs Predator, Serenity, King Arthur, League of Extraordinary Gentlemen and many more.
What the heck just happened? The Alien attacked the Predator, but then it was all blur fu.