PBR has two main workflow options: Metalness and Specular.
Switching between workflows will change the workflow for ALL materials in the model.
Metalness
The channels specific to Metal/Roughness are Base Color, Metalness, and Specular F0.
Base Color: an (s)RGB texture or solid color for reflected color (non-metals a.k.a. 'dielectrics') or reflectance values (metals)
Metalness: a linear grayscale texture; black (0.0) for non-metal and white (1.0) for raw metal
Specular F0: a linear grayscale texture for Fresnel values (non-metals)
Specular
The channels specific to Specular/Glossiness are Albedo and Specular.
Albedo: an (s)RGB texture or solid color, without reflectance values
Specular: an (s)RGB texture or solid color for reflectance values (metals, color) and F0 (non-metals, grayscale)
Base Color and Albedo are more or less synonymous. All other channels are common to both workflows.