- photorealism
A rendering system has achieved photorealism when it can render a still image that is essentially indistinguishable from a real photograph.

- lighting model
A mathematical model that defines how light is absorbed and reflected from a surface. This can attempt to model reality, but it does not have to.

- light source
Mathematically, this is something that produces light and adds it to a scene. It does not have to be an actual object shown in the world.

- light intensity
The intensity, measured in RGB, of light emitted from a light-casting source.

- angle of incidence
The angle between the surface normal and the direction towards the light.

- diffuse lighting
A lighting model that assumes light is reflected from a surface in many directions, as opposed to a flat mirror that reflects light in one direction.

- Lambertian reflectance
A particular diffuse lighting model that represents the ideal diffuse case: lighting is reflected evenly in all directions.

- surface normal, normal
The direction that a particular point on a surface faces.

- Gouraud shading
Computing lighting computations at every vertex, and interpolating the results of these computations across the surface of the triangle.

- directional light source
A light source that emits light along a particular direction. Every point in the scene to be rendered receives light from the same direction. This models a very distant light source that lights the scene evenly from a single direction.

- vector dot product
Computes the length of the projection of one vector onto another. If the two vectors are unit vectors, then the dot product is simply the cosine of the angle between them.

- transpose
A matrix operation that flips the matrix along the main diagonal. The columns of the original matrix become the rows of the transpose.

- inverse transpose
A matrix operation, where a matrix is inverted and then transposed.

- interreflection
Light that reflects off of multiple surfaces before reaching the viewer.

- global illumination
A category of lighting models that take into account lighting contributions from interreflection.

- local illumination, direct illumination
Lighting computations made only from light sources that cast light directly onto the surface.

- ambient lighting
A lighting model that models all contributions from interreflection as a single light intensity that does not originate from any particular direction.

- mesh topology
The interconnected nature between different values of a vertex attribute in a mesh. Each attribute has its own separate topology. Rendering in OpenGL requires finding all of the unique combinations of attributes and building a new topology out of it, where each attributes topology is the same. This can require replicating attribute data.