Piston engines are typically arranged with their pistons in rows, moving inside individual cylinders. This allows the engine block to be built from a single piece of metal, which is machined. Engines often have more than one row of pistons, each with their own block, and these are referred to as cylinder banks.
Note that not all engines have cylinder banks. Radial engines have each piston in a separate cylinder, and this was common in earlier in-line engine designs as well.
