Fūinjutsu

are a type of jutsu that seal objects, living beings, chakra, along with a wide variety of other things within another object. An imbalance is created when an odd-numbered seal is placed on top of an even-numbered seal and vice-versa.

The Uzumaki Clan of the Hidden Eddy Village in the Land of Whirlpools were specialists in the art of Fūinjutsu, to the point that they were eventually destroyed due to the fear others had of their sealing techniques.