What's a bank memory? I've search on Google but still don't understand. I've read about it into arm book, but they don't define it.

Could you explain me what is it, where is it used, what's the point to have it and, if you can, its used into arm chips.

Thanks.
Memory banks were an abstraction paired with a hardware implementation to extend the amount of memory normally available to a particular architecture.   

For example, the PDP-8 had a "page" size of 128 12-bit words, and most instructions could only address memory on the same page as itself.  Other instructions could access the full memory complement of 2^12 (4K!) 12-bit words.  To go beyond 4K, special techniques could address memory outside the normal 4K. When implemented, the original 4K became (memory) bank 0 and other
memory banks numbers 1, 2 etc might exist.

The details varied, as computers worked their way up to today's standard
of 64 bit address space.