Extreme of Corner
Extreme of corner averaging means that the extreme value from all the corners of an element are extracted and the value is shown at the centroid of the element.
For example, as shown in Nodal Averaging of Elemental Results, there are four tensors at each corner of the element A: [A1], [A2], [A3], and [A4].

This averaging option is only available when the Use corner data option is checked in the Contour or Iso panels.