Backing is not a combination of multiple parts, but the first step before installation. It is to paste several layers of rice paper on the back of calligraphy works (also known as painting cores). The first layer of rice paper must be dried before the second layer can be pasted, and so on. The specific number of layers depends on the need. If you say album pages, you often need to paste seven or eight layers, or even a dozen layers.
After the bottom support is completed, it is the back cover. If it is a vertical shaft or banner, it is the edge of silk. If it's an album, as you said, the supported pages at the bottom are spliced together to form a whole.