As the title.
Collider.material is a reference to the specific material applied to the single model.
Collider.sharedMaterial is a reference to the material used by all members of that model.
Assume you have two instances of a prefab in your scene. Collider.material reference will allow you to change the values of one without changing the other while Collider.sharedMaterial would allow you to modify both (or all) instances in the scene.
I see.Thank you very much.
How was this not clear fro the manual? Log a bug if you think BPPHarv told you something that wasn’t documented.