What are Tailed Beasts and Jinchūriki

Jinchūriki "Jinchuuriki" meaning the "power of human sacrifice", are those individuals possessing tailed demons within their bodies. The demons themselves are known by the number of tails their body possesses, and each has different characteristics. The only known named Jinchuuriki are Gaara of the Sand, Nii Yugito, Yagura, Roushi, Han, Utakata, Fuu, Killer Bee and Uzumaki Naruto.

Bijuu

The bijuu are creatures of great power and destruction, and all the ninja nations coveted that power and sought to make it their own as weapons. To that end the various bijuu were captured and the ninja nations attempted to use that power. This unimaginable power proves difficult to manage however, requiring literal sacrifices to gain control. Several jutsu variations have been used to seal a bijuu within a human. Yondaime Hokage used his Shiki Fuujin technique to capture the rampaging Kyuubi and seal it within Naruto. The jutsu had a high price, resulting in the death of the jutsu's user, Yondaime Hokage. The Ichibi Shukaku was sealed into the unborn body of Gaara, with the sacrifice taking the form of his mother, who died as a result of his birth.