Are shadows rendered by mesh, or Tris/Verts?

I am using mesh combiner I made. he only problem is, I dont know it shadows are rendered per mesh ,or per verticy rendered.

From this article on Shadows in Unity from Unity manual it states that:

Unity uses so called shadow maps to
display shadows. Shadow mapping is a
texture based approach,

And as per the Wikipedia link for the Shadow mapping from the same link above. It states that:

Shadows are created by testing whether
a pixel is visible from the light
source, by comparing it to a z-buffer
or depth image of the light source’s
view, stored in the form of a texture.

Which means shadows in Unity are calculated based on pixels.