The following definition was posted here a while back by John Farley. I quote:-
"A wingover is just a turn through 180 degrees that is started from a climb and finished in a dive.
For this manoeuvre to count (in the eyes of a casual observer) as a wingover it will probably have to start from a minimum of 45 deg climb and finish with a minimum of a 45 deg dive."
See also the following, from an aerobatics FAQ at
http://acro.harvard.edu/ACRO/faq_aerobatics.html#basics
Wing Over
The Wing-Over is a competition maneuver in glider aerobatics. You pull up and at the same time bank the plane. When the bank increases past 45 degrees, the nose will start to drop while the bank keeps increasing and the plane keeps turning. Halfway through the maneuver, the plane has turned 90 degrees, the fuselage is level with the horizon and the bank is 90 degrees. The plane is above the original flight path. The nose then keeps dropping below the horizon and the plane keeps turning, while the bank is shallowed. When the bank drops below 45 degrees, the nose is pulled up towards the horizon and the plane reaches horizontal flight with wings level after 180 degrees of turn. At the completion of the maneuver, the plane is at the same altitude as on entry and flying in the opposite direction.