What is another name for a waffle slab?

A waffle slab is also known as a two-way joist system due to its design characteristics. This type of slab features a grid-like structure that consists of a series of ribs, which provide support in both directions—hence the term "two-way".

The two-way joist system effectively distributes loads across the slab, allowing it to span larger areas without needing as much material as a solid slab would. This makes it an efficient choice for creating open spaces in building designs, such as in commercial structures where large floor areas are desirable.

In contrast, a one-way joist system primarily supports loads in one direction, which limits its application for larger spans. A flat slab, while also efficient, does not have the ribbed structure characteristic of a waffle slab. Similarly, a composite slab generally refers to a system that combines materials, often steel and concrete, but does not specifically pertain to the two-way load distribution feature of a waffle slab.