What are PBR models ?

Hello there! :)
If you search the forum several people explained it already. PBR is short for "Physical Based Rendering" meaning materials are setup so they behave like in real life when they are exposed to light (e.g. how they reflect / refract / transmit / scatter light) and much more. There are great articles on the internet if you want to get into mathematics behind it if you want to get into detail. Depending what materials people use for their objects they need to deliver the needed maps (e.g. a metallicity map for an object made only out of wood wouldn't make sense since it would be just a black map).

The thing is there are these two different PBR shading types.
Specular/Gloss versus Metallic/Roughness.

Typically the texture maps from a model intended for those types of PBR rendering are going to have maps including naming conventions Color, Specular, Gloss, Roughness or Metallic, etc. The numeric values of such a shader are usually going to be controlled with the gray levels of those maps (exception in Metallic/Gloss, metallic channel can also have color) in order to have a consistent look (no need to manually manipulate values).

In ideal situations you just need to plug the maps in associated slots and the shader should render as intended. Basically in this case the textures (if done correctly) are in some sense the shader (control shininess, metallness, roughness, etc.).

So if you have a Gloss map, Metallic or specular map specifically made for these types of PBR shading then you can call your model a PBR model (if I'm correctly).

If you have specific shaders setup for physically based shading like in Octane render or Vray, etc., and included those shaders, then I believe you can also call it a PBR model, but not so sure about that.

If I understand correctly its just those specific textures that need to be there.

Thank you for your detailed answers ! Yeah I think PBR tag on models only make sense if PBR textures maps like metalness roughness, as you mentioned, are provided.

IterateCGI is correct. There needs to be specific texture maps for a model to be considered "PBR" ready. He mentioned the two different PBR workflows - Specular/Glossiness (which is used mostly by physical path tracing render engines), and Roughness/Metallic (which is usually used by game or real-time render engines). These two workflow types can be interchangeable, and some render engines can use both a roughness/metallic and a specular/glossiness (Blender's Principled Shader can use all of the above to create materials). The color maps in a true PBR workflow are called Albedo maps. These are strictly flat color representations of the material, and should never contain specular or shadow components in the color channels. Normal Maps are probably the most common component to any PBR render engine. They are used in both path tracing and real time PBR render engines. A height map for displacement is also a handy element to include if possible, esepecially if you're dealing with path tracing render engines.