Physically Based Rendering (PBR) is tossed around a lot by artists and job advertisers. To many people, PBR is the wave of the future that you had better be on, or become a dinosaur in the industry. However, that is not true. It is not true because PBR is not a style of texturing. Rather, PBR simply means that the rendering engine interprets the texture inputs in a physically based (physically accurate) way based on how light interacts with real world materials. For a full guide, you may read up further in the following resources, but let’s unpack this a little first.
You already know from Texture Types that a texture is an image input that tells the rendering image how to display the model. There are many texture types, some of which correspond with the PBR approach to texturing, and some that do not. In the PBR approach, we are not stopping at creating textures, but instead must compose materials.
A material is a substance like oak wood, burnished steel, a composite such as plastic or other. Materials in 3D graphics are made up of multiple texture inputs, among which are the albedo, normal (if present), ambient occlusion, metalness , roughness (note that this is the inverse of a specularity map) and others. There are two (2) general approaches to a material in video games:
Ultimately, the end result is to achieve consistent and good lighting that is part of the artistic vision. If using a PBR approach, the lighting of a model may be calculated accurate to a physically based material, but if the artist desires a different look then they may knowingly deviate from expected values to achieve such a look.
Physically Based Render Chart, Google
Physically Based Render Chart for Unreal Engine 4, DONTNOD Entertainment