In Lakota tradition, Skan is the Motion of the universe. The Great Spirit, Wakan Tanka, reflected upon himself and created the four Superior Spirits, Wi (the first to be created, bringing light to the world), Skan, Maka (Mother Earth) and Inyan (the solid support of the Earth or the rock associated with the natural forces of the Earth).
Skan enters the body with the spirit and sets new life in motion. All that is created is in motion, to the radiance of the One who created all things, Wakan Tanka.
The above taken from Chief Archie Fire Lame Deer and Helene Sarkis (1994) The Lakota Sweat Lodge Cards: Spiritual Teachings of the Sioux Destiny Books ISBN 0-89281-456-X