Let me do a little correction.....

Tai Chi is a form of martial art but has been watered down to just a bunch of slow movements. Many of the forms these days are made up and has no relationship to the original Tai Chi which is Chen Tai Chi. A very good example is the 24 movement form of Yang Tai Chi. It was created by the Chinese government and the organization that the Chinese government created is called Wushu. This is better left off as another topic.

Tai Chi is also a form of Qi Gong. The Tai Chi form can be used to do either martial arts (self defense) application AND also as a way to move the Qi in the body. That is why you need to seek a good master to teach you this.

Qi Gong is NOT a martial art. Qi Gong are simple movements to move Qi for health. It can strengthen the body function by moving the Qi in the body. Qi Gong provides the foundation for many Chinese martial arts.