Physically-based rendering or PBR is an umbrella term that encompasses tools and techniques that make use of physically-based models of light and reflection. The term itself is somewhat loosely defined, but can generally be described as a shading/reflection model that tries to model the physics of light interacting with matter as accurately as possible. The term may mean slightly different things to different people, but for our purposes, we are interested primarily in how it differs from the Phong and the Blinn-Phong reflection models.
The Blinn-Phong model is an empirical model of reflection based on observation. A PBR model could also be considered an empirical model, but in general, it is more detailed ...
