A question about the limitation of terrain layers

https://docs.unity3d.com/Manual/class-TerrainLayer.html
I dont understand this part:

what does the "texture pass" mean? is it "the neighbor terrain"?If I want to paint more than 4 layers,I have to add more neighbor terrains and paint there ?

 

You can paint more than 4 layers at the same terrain
However Unity can render the terrain in 4 layer batches. If you have more than 4 textures on a single terrain Unity will have to repeat the render process again, meaning the render time for the terrain will increase

 

Hi

Is there a way to limit the passes unity uses if using a single pass shader but have more than one pass textures active ?