Hijutsu (Secret Techniques) or Hiden (Secret) refers to the techniques that are passed down from generation to generation in certain regions or clans.
The groups possessing these techniques are usually extremely secretive about them, ensuring no-one other than the members of the group learn them. Only a scarce few Hijutsu require a special ability or lineage, but they are simply not taught to those outside the group. These Jutsu are usually the pride and fame of the clans that possesses them.
Kekkei Genkai Edit
Kekkei Genkai (Bloodline Limit) 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, although Kakashi has to use extra chakra. Kekkei Genkai abilities that work via the user's eye are called Dojutsu.