pole vector

In animation, a part of an IK rotate plane handle that begins at the start joint, and along with the handle vector defines the IK handle’s reference plane.

The pole vector changes the orientation of the reference plane, so can change the orientation of the joint chain directly. This is because the joint chain’s degree of orientation, or twist, is defined as the difference in orientation between the reference plane and the joint chain plane.

In other software packages, known as up-vector.

See also pole vector constraint.