Split bone breaks the selected bone(s) using the interactive Split Bone widget. Clicking and dragging the widget will move it along the bone. Simply clicking will create the split.
Merges two selected bones, if they have a parent/child relationship.
(default keyboard shortcut Ctrl U)
(Setup > Detail > UnParent Bone) The selected bone’s relationship with its parent bone (if there is one) is severed, and it is parented to its object. After being “unparented”, the selected bone’s rest position is edited so that it remains in place, not moving, with respect to global coordinates.