A memory bank is a logical unit of storage in electronics, which is hardware-dependent.
In a typical synchronous dynamic random-access memory (SDRAM) or double data rate SDRAM (DDR SDRAM), a bank consists of multiple rows and columns of storage units, and is usually spread out across several chips.
In a single read or write operation, only one bank is accessed, therefore the number of bits in a column or a row, per bank and per chip, equals the memory bus width in bits (single channel).
The size of a bank is further determined by the number of bits in a column and a row, per chip, multiplied by the number of chips in a bank.
When data is stored or retrieved consecutively each bank has enough time to recover before the next request for that bank arrives.