What's a bank memory?
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.