what's the difference between Bone and Joint in Skeleton while rendering FBX model?why most toturials have Bone but no Joint class?

Question

what's the difference between Bone and Joint in Skeleton while rendering FBX model?why most toturials have Bone but no Joint class? how to animate a FBX model imported by Assimp(which only has Bone but no Joint) by manually update Joint data every frame? thanks