This is a sealing technique based on the fūinjutsu of Uzushiogakure's Uzumaki clan. The sealing formula is used to seal any target into a human body or an object, and is mainly used when a giant enemy or evil spirit needs to be sealed away. To use it, it is necessary for the user to have great ability.
When two Four Symbols Seals are used together, they form the Eight Trigrams Sealing Style. When Minato Namikaze sealed Kurama into Naruto Uzumaki, he left an opening at the space where the two seals met, allowing Kurama's chakra to mix with Naruto's own. Minato also left behind a key with Gerotora, which could be used to freely manipulate the seal.