Let's keep it simple:
Abnormal foot pronation (during stance phase of gait) is any pronation that is occuring when the foot should be supinating.
According to the research of Inman and Close, the pelvis (transverse rotations) should drive the motion in the foot: Internal pelvic rotation will pronate the ipsilateral (same side) foot. External pelvic rotation will supinate the ipsilateral foot.
From heel contact to foot flat, the foot should be pronating.
Any pronation past foot flat, is by definition, abnormal pronation.
For more information on abnormal pronation, read the discussion of the Podiatry Forum at: http://podiatryarena.com/index.php?threads/defining-abnormal-pronation.111866/page-2