Kinjutsu

are techniques that have been banned from being taught or used.

This ban could have been put in place for any number of reasons, but kinjutsu can generally be put in either of two categories:
 * 1) Techniques that do extreme harm to oneself (e.g. the Multiple Shadow Clone Technique, which will bring almost any user to the brink of death by mere use).
 * 2) Techniques that violate the laws of nature (e.g. the Summoning: Impure World Resurrection, which resurrects the dead with a human sacrifice). EX: Izanami is used by Uchiha Itachi and can alter reality in exchange for one's vision. Izanagi was used by Danzou and he was able to change his death into just an illusion.

Despite being banned, the use of these techniques generally does not carry any legal consequences in respects to the village they're used in, except those brought on by the techniques themselves. However, their use is heavily frowned upon, especially those techniques that violate nature.