Short answer
Subclass 117 is a permanent child visa for a child outside Australia who cannot be cared for by either parent and has an eligible Australian relative.
The subclass 117 Orphan Relative visa is for a child who is under 18, has no spouse or de facto partner, and is the relative of an eligible Australian relative.
The child must be unable to be cared for by either parent because each parent is dead, permanently incapacitated or of unknown whereabouts.
The visa also requires that there is no compelling reason to believe that granting the visa would not be in the child's best interests.