Sanchindachi

Sanchindachi is one of the stances of GoJuRyu, and perhaps the most important.  It is done with the feet shoulder-width apart, one foot in front of the other, the heels turned slightly outwards (so that two imaginary lines extending in the direction the toes are pointing would intersect directly in the center of one's opponent's body). The toes are opened, not clenched, and grip the floor, generating a slight torque which is maintained up the inside of the legs and into the buttocks and tanden. 

The center of gravity is kept low and the body "locked up" to make the stance a strong one.  C. W. Nicol puts in nicely in Moving Zen, his account of studying Shotokan in Japan in the 1960s:

"The stance of the Karateka roots him to the earth at the moment of impact. For a split second in time he is a statue, like a stone from the earth, and then, after the blow is delivered, he relaxes and his body recoils in preparation for the next move, taking more of the water from from which most of his body is made up. Stone, earth, water. Movement and non-movement."

However, with sanchindachi, there is no relaxing - the tension is maintained throughout