A hoop direction applies to axisymmetric models and is the Global Z axis and represents the tangential direction around a circular object that is being viewed in a radial slice. In Axisymmetric models, circular objects are implied by rotation about the Global Y axis.

In Plane Stress, you are not required to have any circular objects. If you draw a circular object in the XY plane, you can put a Cylindrical Coordinate Sytem at the center of the circle. Make sure the Z axis point out of the plane. Now the X axis is Radial and the Y axis of the local cylindrical coordinate system is tangential to the circle.