Kekkei Genkai

are abilities passed down genetically in specific clans. Kekkei genkai and their related jutsu can't be taught or copied by others, but it is possible to confer the ability to another person if it's localized in a particular organ like the eyes via organ transplant, like Obito passing his Sharingan eye to Kakashi. Kekkei genkai abilities that work via the user's eye are called dojutsu.

Kekkei genkai should not be confused with hiden jutsu. Hiden jutsu are exclusive to a certain person or clan, but only because they have kept others from learning how to perform those jutsu.