These are 2 related features. I'll describe them below.



Scene Layers: This is the ability to select objects and assign them to named layers. So, I could put all my trees and foliage on a layer, enemies on another layer, buildings on another, and so on.



Visibility by Layer: This would allow me to select which named layers that I currently want visible in the editor. This makes it easy to turn off a lot of clutter and just focus on what I'm working on at the moment.



These are all typical features found in game editors and 3D packages.