Fuuinjutsu, so what i gathered is that through the use of kanji codes or spells you seal chakra, living animals or "beings", objects and energy through a medium to another object like a scroll or a tatoo on your body. Through these kanji codes or spells, you expand the chakra to activate them and also to sustain the spell. Now you can release it by the use of chakra or provided with a correct key like as it was seen when unsealing the 9 tails from naruto or you can also provide a dna imprint through the blood contract. There are many different applications, though the concept is the same or similar in general. You need chakra to be able to do it and sustain it while needing a medium of sort. Though because of chakra usages to seal something and sustain it, overtime the seal gets weakened, as one would see through the manga or anime. I don't know any real history behind it besides that kushina where ever she came from, they were good at fuuinjutsu.