What is Taijiquan?
Taijiquan – also written alternately as taijiquan, t'ai chi and tai chi chuan – is an "internal" (wudang) Chinese martial art (in contrast to the "external" (shaolin) Chinese martial arts. The distinction being looked upon today as a perhaps unnecessary, hair-splitting argument that took place within China's martial arts community of the period 5th century CE, regarding whether the focus should be on mastering strictly the physical techniques associated with martial arts, or mastering these in connection with the mastery of one's own unique abilities, or 'getting in touch with one's qi', or life force, as it were, in a mind over matter sense).
The seemingly unnecessary distinction was not unimportant, however, especially at the time (and may still apply), since, due to the widespread popularity (both then and now, one might add) of the martial arts, or wushu, there was a creeping tendency (perhaps a galloping tendency today) toward "cutting corners", or only learning the more macho, or aggressive, side of wushu disciplines. The internally focused, meditative side of wushu that was aimed at harnessing the qi had unfortunately become neglected, if not entirely ignored. The emphasis on the internal forms of wushu was therefore introduced in order to redress this shortcoming.
Some practitioners of wushu, especially those with an interest in China's earlier, homegrown religion, Taoism (Taoism, alternatively, Daoism, was as much a philosophy as a belief system), likened the distinction between the internal versus the external forms of wushu to the distinction between the yin ("dark", "cold") and the yang ("bright", "hot – though the yin and the yang could represent any particular set of seemingly opposing concepts such as good verses evil, male versus female, etc., the point being that the two were in fact intimately intertwined, or 'two sides of the same coin', as is suggested by the yin and yang symbol itself).