Tai chi is an internal Chinese martial art. Tai chi is typically practiced for a variety of reasons: its soft martial techniques, demonstration competitions, health and longevity.

T'ai chi is a Chinese exercise system that uses slow, smooth body movements to achieve a state of relaxation of both body and mind.

the five essential qualities of t'ai chi are:

* Slowness. To develop awareness.
* Lightness. To make movements flow.
* Balance. To prevent body strain.
* Calmness. To maintain continuity.
* Clarity. To focus the mind.

Tai chi chuan is classified as Wudangquan or an internal Chinese martial art. Tai chi is typically practised for a variety of reasons: its soft martial techniques, demonstration competitions, health and longevity. Consequently, there exist a multitude of training forms, both traditional and modern, which correspond to those aims. Some of Tai chi chuan's training forms are well known to Westerners as the slow motion routines that groups of people practice together every morning in parks around the world, particularly in China.

Today, tai chi has spread worldwide. Most modern styles of tai chi trace their development to at least one of the five traditional schools: Chen, Yang, Wu/Hao, Wu and Sun. Who actually created tai chi is a subject of much argument and speculation. However, the oldest documented tradition is that of the Chen family from the 1820s.
source wikipedia

http://en.wikipedia.org/wiki/Tai_chi_chuan