Tai Chi is made up of different styles, which are practiced slightly differently from one another. There are hundreds of different styles in existence, but only five major styles. They are named after the families that created them: Chen, Yang, Wu, Sun, and Wu-hao. Chen is the oldest style and is the most like Kung Fu because it is still deeply rooted in self-defense applications. Some of the other styles are more oriented towards health (although they can still be used for self-defense, but just aren't as explosively martial as Chen-Style).
A typical description of a person practicing Tai Chi would look something like this: The Tai Chi practitioner drops down into a low stance and begins to practice. Precision, concentration, balance, and poewr are all evident in the practitioner's movements. Unlike Kung Fu, Tae Kwan Do, or Karate, however, this person moves very slowly, as if through molasses. The movements are a series of blocks and attacks strung together and practiced as if fighting invisible opponents in slow motion.
For a great video clip of a man doing Tai Chi, check out this YouTube address: http://www.youtube.com/watch?v=sqGooDkDQHg
