Works by: Drag and drop, right-click
Hot keys: Command+X
Source requirements: One or more source relationships required
Target requirement: One target required
The move operation removes a parent relationship from a term, and creates a new relationship with a different parent. The move operation is analagous to an of "Add Child" operation and a "Delete" operation from the original parent.
To move one or more relationships, select a collection of source relationships that you would like to move. Then, select a target term to which they will be moved by right-clicking the target term or by drag-and-drop.
The move menu item has a flyout submenu of the relationship type that should be used when creating the new relationships:

Select the relationship type you would like for the new relationship, and it will be created. If you would like the new relationship to use the same relationship type as the original source relationship, use the "Use original type" menu option. This is particularly useful if you are creating several relationships at once by using a number of source relationships. If "Use original type" is used with untyped source relationships (ie one or more of your sources is an ontology root) the is_a relationship is used.
When dragging, you can use hotkeys to specify the "Move" edit operation.
To specify "Move", press the "Command" and "X" keys on the keyboard, then start dragging. The hotkey dropdown menu will change to "Move" and title above the terms you are dragging will change from "Dragging" to "Move..."

Note that if you want to use hotkeys to drag from one Ontology Editor Panel to another, you must specify the "Move" operation in both Ontology Editor Panels.
You can also use hotkeys to choose which relationship type will be assigned when you drop the dragged terms. Each relationship type is assigned a hotkey (Command+another key, usually just the number that corresponds to the relationship type's position in the list, but IS_A always gets the hotkey "I").