How to give an object alpha material? I'm currently using a plane to conceal a few meshes in my scene (i'm using Cycles). This plane has a white emission surface, the same color as the background.

Is it possible to, instead of using a white material, give this plane an alpha material? Anything hidden behind this plane should thus not render.
It's worth mentioning that some objects are only partially concealed by the plane, thus I can not simply remove it from the scene.

For example:

In the image, I have a scene with two cubes, a plane and a monkey. The plane currently has an "alpha" shader/setting (this is the thing I want) assigned to it.



When rendered, the scene will look something like this:



Anything behind the plane will disappear from the render, whilst anything in front of it will not be affected.

It's worth mentioning that some objects are only partially concealed by the plane, thus I can not simply remove it from the scene.
Instead of an emission shader just add a "Holdout" shader and anything behind it will be left out.