My understanding - a PowerWall is just the product name of Tesla's battery bank. Then there are other "power walls" that are by other companies. They tend to have the AC coupling inverter built in. That's all, really.
A PowerWall(tm) is ~13kWh with a 5kW inverter integrated into a box. If you need more storage, you AC-couple multiple together. A battery bank can be many different sizes, and when you need additional storage you DC-couple the batteries together. An external inverter or paralleled bank of inverters provides the AC power for your loads from the common DC bus.
The main advantage of a manufactured assembly is that it is warranteed and supported unit, generally UL-listed, and can be installed by a professional. A DC battery bank generally becomes more of a DIY effort, but the advantage is that it is easier to size both the battery and inverter capacities to meet your specific needs.
I use the generic term powerwall sometimes, thinking of DIY battery banks that are larger / permanent as part of a fixed solar system for a building.
Battery bank describes itself - e.g. a group of batteries but Powerwall is not so clear. In my mind, a battery bank can become a powerwall when it's part of a fixed Solar installation. But agree it's not clear