A subgenre of kung fu films. Wire fu employs a cinematic technique ("wire work") where complex wire & pulley systems are used to give the appearance that the martial artists on screen are literally defying gravity. Warriors walk on walls, leap dozens of feet through the air, and launch into mind-boggling kung fu sequences that leave you thinking that the Laws of Physics were made to be broken.
Though Crouching Tiger, Hidden Dragon is probably the best-known and most popular movie in the genre, it wasn't nearly the first to use wire fu techniques. Kung Fu legends Jet Li and Yuen Woo Ping are usually credited for inventing the techniques in Hong Kong, during their work on dozens of kick flicks in the early 90's. Some outstanding wire fu flicks from this era include: Fong Sai Yuk, Tai Chi Master (aka Twin Warriors), Butterfly & Sword, and Iron Monkey (which was re-released in America just this weekend).
Li's classic Once Upon a Time in China series is also interesting to watch in this regard. You can clearly see how the wire fu enhancements of traditional Kung Fu techniques become more and more prevalent as the series progresses.