Shinobi-no-jutsu, more popularly known as ninjutsu, was not a martial art. It was a system of duplicity and grand deception coordinated through the aid of a larger army to which the shinobi owed allegiance. The Bansenshukai, Shoninki, Ninpiden, Gunpo Jiyoshu, and other scrolls iterate the point that ninjutsu was an auxiliary art to the already formidable skillset of the samurai.
RE: Ninja or Shinobi