Ninjutsu is best described as the collection of skills utilized by the Ninja while Ninpo, often referred to as "the higher order of Ninjutsu," implies a philosophy for living based on the principles of Nin.
Nin translates into patience, but can also imply perseverance, or stealth. The Japanese character for Nin consists of two parts or radicals. The upper radical is called yaiba which refers to the cutting edge of a blade. The lower radical can be read either as kokoro or shin, both of which mean heart.
The character po, which implies natural law, is used rather than do (i.e.. judo, kendo, aikido,etc). Referring to our art as Ninpo rather than Ninjutsu stresses training which is concerned with the internal development of the individual's character along with the technical skills of martial training. It isn't enough just to know techniques, it is where your heart and spirit are as a person that is important. For this reason, Ninpo stresses philosophic and spiritual training in conjunction with the physical training. This refinement of one's spirit is known in Japanese as seishinteki kyoyo.
Ninpo is concerned with the defense of the whole self, and recognizes that defense against a life-threat is dealt with by the spirit as much as with physical technique