Bank 2 on an engine refers to one side of a V-type or horizontally opposed engine. In a V-engine, it's the side of the engine opposite bank 1. In a horizontally opposed engine, it's usually the right side (as viewed from the driver's seat).
Essentially, it's a way to differentiate between the cylinders on either side of the engine's centerline. Diagnostic trouble codes (DTCs) often specify Bank 1 or Bank 2 to indicate which side of the engine is experiencing a problem.
