Design Nomenclature / Form & Geometry
Normal
Also called surface normal, face normal, vertex normal, winding order, face orientation
This entry has not been translated yet and is shown in English.
The unit vector perpendicular to a surface at a point, fixing which side is outward. A face normal follows from the winding order of its vertices — counter-clockwise seen from the front, by near-universal convention. A vertex normal is a weighted average of the adjacent face normals, and it, not the face normal, drives smooth shading.
In practice
'Flipped normals' means reversed winding, not a corrupted vector; the fix re-orders vertices. Backface culling, boolean sidedness, draft analysis, and a slicer's inside/outside test all read this one value.