Blinn-Phong
A reflection model that approximates specular highlights with a halfway vector — a cheaper variant of Phong's model.
Jim Blinn's 1977 refinement of Bui Tuong Phong's 1975 shading model. Phong derives the highlight from the angle between the reflected light and the view direction; Blinn instead uses the halfway vector between light and view, which is cheaper and, with directional lights, needs no reflection vector at all.
The result is a slightly broader and often more convincing highlight. Blinn-Phong was the built-in lighting model in OpenGL and Direct3D for two decades and is still the textbook starting point before physically based rendering takes over. It isn't energy-conserving, so modern engines moved on to microfacet BRDFs.