PBR Texturing is the process of creating digital two-dimensional images which store surface and color information which will be projected onto a 3D object.
The most popular PBR workflows that are used are Metallic/Roughness and Specular/Gloss. Depending on which workflow you use will depend on which maps are used.
Metallic/Roughness: Base Color, Metallic, Roughness, Normal, Height
Specular/Glossiness: Diffuse, Specular, Glossiness, Normal, Height
Additional maps would include Ambient Occlusion, Displacement, Emissive, Subsurface Scattering.
Metallic maps only use black and white inputs which determines which areas are metal and which are not metal (white for metal, black for non-metal), and the color of the metal is controlled by the Base Color Map. The Specular map, on the other hand, has color in it and this controls the colour of the metal and not from the Diffuse map.
There are other software packages which allow artists to create custom tileable, modular and dynamic materials such as Substance Designer. These can then be taken further into Substance Alchemist to blend layers of different materials which is generally used for exploration when creating a scene.
Below are some examples of some realistic and stylised PBR shaders which use a selection of workflows and maps outlined on this page.