Answer
In the context of liquefied gas carriers, "Prismatic" refers to the geometric shape and design framework of the cargo containment tanks. Specifically, it means the tanks are constructed with flat surfaces and straight edges (forming a prism-like shape) designed to conform closely to the internal profile of the ship’s hull.
This design maximizes the volume of cargo the vessel can carry compared to cylindrical or spherical tanks, which leave significant empty spaces (broken stowage) inside a rectangular hull.
Under the IGC Code, prismatic tanks are classified as Independent Tanks (self-supporting tanks that do not form part of the ship's hull structure). They primarily fall into two categories: Type A and Type B.