How to interpret the term "region" and "layer" ?

Hello !
I am wondering the term “region” and “layer” apreaed in the white paper or HTM.JAVA project realy mean, in the, you can create multi-region network, and multi-layer network, I don’t know the differences between them in the data structure and in the concepts.
The layer or region in the white paper is descrbing the same concept, the region is derived from the biology term, they are the same meaning, however in the project, they seems differnt. How can I understand the region and layer.
In the HTM.JAVA project, my understand is the SDR is a region and a layer contains multiple regions, and multiple layers compose the hierarchical structure. Howerver, in the HTM.JAVA project, the region seems contain multiple layers, and each layer contains a SDR.
any explanation is appreciate!

I think @bitking gave a great answer to this question on this thread.