Surface normal

Imagine you are standing in front of a wall. If you touch the wall with your hand, you can feel that it is flat. But did you know that the wall also has a direction? This direction is called the "surface normal".

The surface normal of a flat object or surface is the direction that is perpendicular (like a T) to that object or surface. So if you imagine drawing a line directly out of the wall at a 90-degree angle from the surface, that line would be the surface normal.

Surface normals are important for 3D graphics and animation because they help determine how light reflects off of an object. If an object is facing towards a light source, it will reflect more light and appear brighter than if it is facing away from the light source. The surface normal helps to calculate this effect.

So, to sum up: a surface normal is the direction that is perpendicular to a flat surface, and it helps determine how light reflects off of that surface.