From SotS

Weapon Banks are linked weapon mounts. Physically close turrets are organized into "banks" of weapons that all are equipped with the same weapon choice and all concentrate fire at the same target point chosen by the player.

Think of them as the row of cannons on an old man-of-war that all fire together every time. So, for example, the Human Hammerhead Command Section only lets you pick one weapon type for that section while the Liir version has the same amount of turrets but you can pick different weapons for each of them and they will select targets independently. A subtle but sometimes important difference.

Personal tools
SotS 2 Codex