The Martial arts term for Ninjutsu literally means skills of perseverance.
Historically, Ninjutsu is a general term for a variety of martial skills that share a common characteristics.
These characteristics include the people who nurtured and developed Ninjutsu, the combination of conventional and unconventional fighting methods, and the period when Ninjutsu was most widely used, among other characteristics.
Disappearing techniques utilize surprise, technical body maneuverability, and the aid of blinding devices or techniques, to “super humanly disappear.
For example, setting off small explosives to create a cloud of smoke, or simply throwing sand at the opponents eyes would provide a warrior the opportunity to hide.
It is common among those who practice ninjutsu these days to think that in medieval Japan the goal was to master all aspects and all the techniques associated with ninjutsu.
However, the movie industry only reflected and exaggerated a common Japanese view of Ninpo/Ninjutsu and ninja that have existed in Japan at least since the early-modern period (Tokugawa/Edo period 1600-1868).
Ninpo includes the eighteen martial skills (bugei juhappan) for the common bushi (warrior), and another group of eighteen unconventional types of martial skills (ninja juhakkei) for special warfare.
Ninpo is a group of related martial traditions that have developed in Japan since the ancient period (before the 12th century), and that have been combined in the modern period under one comprehensive martial system.
Indeed those who were skilled in ninjutsu were proficient in surveillance techniques, but it is a common mistake to view these warriors as professional spies who were groomed since childhood to serve as such.
The truth remains, though, that warriors in Japanese history who applied Ninjutsu were not super-human assassins for hire, rather a group of people who were not confined to common concepts and rules and developed a wider, more effective form of fighting skills.