SharedMesh an explenation for a noob

Well I am having some problems with sharedmesh as an emitter and have some more general questions. I hope U can answer.

What is sharedmesh compared to TriMesh?

When is something SharedMesh?


I had a

And the only difference between the objects is rotation, position, or scale

SharedMesh can also differ on RenderStates

Does shared mesh make a display list and then transform and all that good stuff?

If the target trimesh is locked.