The phrase "thin slab" refers to a flat and relatively thin piece of material, such as metal or concrete. It means that the object is not thick or heavy, but rather thin and lightweight. Full definition
The complex has a series of thin slabs with courtyards in between. (treehugger.com)
I might suggest that you put thin slabs of marble on top of the hanky drawers. (theletteredcottage.net)
The lighter model prevailed, but with engineers developing and testing two competing concepts, they had less time to figure out how to cram all the electronics into a thin slab of aluminum that would hold together. (bloomberg.com)