That is a mouth full…
This variable controls the fade percentage when you lock a layer. You can type this in on the command line and enter anything between zero and 90. If you went above 90 you would not be able to see the layer and you might think it was Off or Frozen.
Below you can see (or maybe not see) the walls and the doors are on locked layers. The top image is with the layers Unlocked and the bottom one is with Locked layers.
The default value is 75 – as shown.
Locked layers that are dimmed are plotted normally.
Note: Grips are not displayed on objects that are on locked layers.