Discarded Worlds exists within an infinite half-space, with one half being complete vacuum and the other half being complete plenum of dense fluid. The closest analog would be an endless sea of infinite distance and depth below and endless sky of infinite height. The interface between the two is known as the Velethe proper, although Velethe can equally be applied to the infinite vacuum or infinite plenum.
Most shards come into emergence at the Velethe and their landmasses "float" on the surface of the plenum. Some shards may be suspended within the vacuum above or embedded within the depths below; shards exist in the velethe within their own context.
The matter composing the plenum is an inky-black low viscosity fluid, almost mist-like at the Velethe. However, the plenum's relative density may manifest differently depending on the context of the shard.
Exposure to the Velethe dissolves everything it touches without the possibility of ever coming back, all that remains is the memory of its existence or any recorded accounts. People or objects cast into the Velethe disassociate almost instantaneously into primordial energy, however some inanimate "world objects" like landmasses, liquids (in particular water), and base materials tend to have a much higher resistance to the effects of the Velethe. Most shards tend to have a barrier or a no man's land where the main landmass of the shard contacts the Velethe. These regions tend to be bleak and lifeless, and prolonged exposure to them can cause a slow draining of one's life force into a hollow echo of one's former self.