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Make a selection in the viewport. Hierarchy panel Pivot button

Every object has a pivot point that represents its local center and local coordinate system.

The pivot point of an object is used for the following:

You can adjust the position and orientation of an object's pivot point at any time using the buttons in the Adjust Pivot rollout in the Hierarchy panel. Adjusting an object's pivot has no effect on any children linked to that object.

NoteYou cannot animate the functions under the Adjust Pivot rollout. Adjusting an object's pivot on any frame changes it for the entire animation. Use caution when adjusting the pivot of an animated object. Adjusting the pivot on one frame might produce unexpected results in another part of the animation. You should adjust the pivot point to the location you want, before you start to animate, if possible.
TipUse the Link constraint to simulate the effect of an animated pivot.