Wikipedia
Neijia is a term in Chinese martial arts, grouping those styles that practice neijing, usually translated as internal martial arts, occupied with spiritual, mental or qi-related aspects, as opposed to an " external" approach focused on physiological aspects. The distinction dates to the 17th century, but its modern application is due to publications by Sun Lutang, dating to the period of 1915 to 1928. Neijing is developed by using neigong, or "internal exercises," as opposed to "external exercises" (wàigōng 外功),
Wudangquan is a more specific grouping of internal martial arts named for their association with the Taoist monasteries of the Wudang Mountains, Hubei in Chinese popular legend. These styles were enumerated by Sun Lutang as Taijiquan, Xingyiquan and Baguazhang, but most also include Bajiquan and the legendary Wudang Sword.
Some other Chinese arts, not in the Wudangquan group, such as Qigong, Liuhebafa, Bak Mei Pai, Zi Ran Men (Nature Boxing), Bok Foo Pai and Yiquan are frequently classified (or classify themselves) as "internal".