This term I have taken liberties with as to meaning. Yes, it means shadow or in my interpretation "to shadow." The shadowing model is one whereby a practitioner shadows a person who they wish to emulate, to learn from and to guide them in an endeavor such as martial arts. It is another way to convey the importance of the sensei-deshi, senpai-kohai, and tori-uke relationship.
A shadow is a silhouette of the person being shadowed. It is a part of that person and makes the relationship one of importance. It is that something one assumes when they acknowledge the presence of the shadow. It is and will be a reflection on that persons efforts to teach, lead and guide in martial arts where the potential brutality of the discipline can be either for good or for evil.
To be a persons shadow, shadowing, is be be in such a close proximity that they will detect everything the person has to offer making the person with the shadow assuming a responsibility that is immense. Immense in that the person is helping the shadow to shape and build themselves into something unique to the shadow, to shed light upon themselves through the teachings and efforts of the person they shadow not to become a mirror image of that person but the use the guidance to build a personal philosophy and moral system that will change the shadow so they become a person who another might wish to shadow.
A shadow is to follow and observe someone very, very closely. It can be likened to that deshi of old Japan martial systems who becomes sensei's personal person not only learning the art but working as the sensei's personal attendant. A deshi or uchi-deshi  who is sensei's "inside student." A live-ion who trains under and assists sensei on a full time basis. The uchi-deshi system existed in ancient Japanese arts such as kabuki, rakugo, shogi, aikido, sumo, and karate as well as other more modern Japanese martial arts.
The shadow, although not actually as complete as the uchi-deshi, still provides a similar relationship that benefits both the person and the shadow. It is a symbiotic relationship where one both grows as one due to the mutual influences they exact upon one another. It is a system that allows the sensei to keep growing toward enlightenment while the shadow learns how to take that path within and upon themselves with a goal of achieving their own path unique to their own cultural beliefs, etc.