To continue what randym77 said: A normal is a vector. It is a vector perpendicular to the plane of the polygon. The direction of the normal (which side of the polygon it points out from) is determined by the order of the points of the polygon. When the polygon is viewed directly from above (so that it appears flat or parallel to the screen, for instance), the common standard is that the points are arranged in a counter-clockwise direction. The normal is then facing directly at you. If they are ordered in a clockwise fashion, the normal points directly away from you. This is why Poser and other apps actually don't need to store normals. They can be calculated from the polygons themselves using the order of their points (vertices). "Reverse normals" changes the order of the polygon's points to flip the direction of the normal.

C makes it easy to shoot yourself in the foot. C++ makes it harder, but when you do, you blow your whole leg off.

 -- Bjarne Stroustrup

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