Reference

Panel:Render Layers ‣ Layer

This section covers only the Render Layer settings appropriate for the Blender Renderer. For the engine-independent settings, see this section.

Exclude
Scene layers are shared between all render layers; however, sometimes it is useful to leave out some object influence for a particular render layer.
Material
Overrides all materials in the render layer.
Samples
Render layer samples to override the scene samples. Controlled by the layer samples in the sampling panel.
Use Environment
Disables rendering the Environment render pass in the final render.
Use AO
Disables rendering the Ambient Occlusion render pass in the final render.
Use Surfaces
Disables rendering object materials in the final render.
Use Hair
Disables rendering hair strands in the final render.