A render pass creates a picture layer of a scene that can be composited with any other passes to create a complete image. Passes also allow you to quickly re-render a single layer without re-rendering the entire scene. Later you can composite the rendered passes using Softimage Illusion, the fully-integrated compositing and effects toolset, or another compositing tool of your choice.

Each scene can contain as many render passes as you need. When you first create a scene in Softimage, it has a single pass named Default_pass. This is a "beauty pass" that is set to render every element of the scene--you can render a single beauty pass or you can render separate passes. Also, you can use preset passes such as matte, shadow, toon, and highlight, or you can create your own passes.

Scene.ActivePass PassCollection Framebuffer