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Here is my previous thread U_U
Ninjutsu is a Nina's way of using his chakra to perform certain tasks. Ninjutsu also exists in real life, but not in the sense you imagine. It is a ninja's way of using deception. They could walk on water using special buoyant shoes. They could disappear in a puff of smoke. The could blind you with a pepper bomb.
In Naruto-verse, it is the art of using chakra to perform basic attacks. Most are taught e ranks in the academy. It is weak to elemental chakra, and to dark release. A lot of ninja can use it to flow chakra into their weapons and make them deadlier. This was seen with the samurai.
That is what ninjutsu is too my knowledge sensei!