What are Bijuu 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. As various clans began to come together as villages, Shodai Hokage sought to stabilize the balance of power. He did so by capturing the Bijuu and offering them to specific villages. This unimaginable power proved 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 his own death. The 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.