Tai Chi (Chinese: “ridge beam”) is an ancient Taoist concept denoting the ultimate and supreme, consisting of yin and yang. In their dynamic combination, yin an yang create the five elements of metal, water, wood, fire and earth, which constitute All That Is. The idea appears in Taoists texts and in a commentary on the I Ching, an ancient philosophical book used for divination.
Phenomenologically, Tai Chi refers to an ultimate mental state or, at least, the highest and most sublime state that the Chinese sages at that time had experienced. We, perhaps, have no way of knowing whether or not this state is experientially equivalent to, say, the Christian experience of heaven.
The ancient Chinese martial art, often called Tai Chi, is more correctly Tai Chi Chuan. The principles of Tai Chi, however, are found within Tai Chi Chaun.