Although it can mean shapeshifting, "shifting" by itself, can be an alteration of the physical body, the soul, mentality, etc., from man into that of an animal.
Shifting is short fo shapeshifting, although the terms transforming, morphing, changing, and turning into can also mean the same thing. There are many forms of shifting and, with it, many interpretations of what shifting is, exactly. To me, it's like the merging of the body and the soul, whether it's spiritual and/or physical.
See also: