Basic Definition
"Void" is a byproduct from the hubstone industry serving as an ideal lighter-than-air substance in numerous industries.
Context
There are numerous hubstone structures throughout the Circlarian Realm each of which contains two components: the core and the web. In Combria, the core is mostly spherical and 100 feet in diameter while the web, made of shale, covers most of the province of Combria. This is just one example of a core-and-web structure, with many others bearing wildly different appearances and size proportions. But for the sake of explaining "void," focus will be given on the Combria structure.
Combria has one of the largest hubstone energy production structures in the world, and begins the process by extracting webstone shale in the form of gas and pipelining it to the Central Hubstone Energy Generation Terminal in Jestopole. There, the shale gas is ignited and superheats the Core in the Central Hubstone Core Chamber. Adapters attached to the Core then conduct the resulting electricity produced to charge hubstone batteries of numerous sizes serving a variety of purposes including the powering of homes and businesses, as well as the powering of numerous appliances.
The Core-superheating process creates three byproducts. The first of which is waste-sludge, a mixture of spent hubstone and water. The second byproduct is electricity, which is produced when the spellfire particles from the Core are split into charged particles and uncharged anti-particles. It is obviously the charged particles that release the energy in the form of electricity. These charged particles are unstable, meaning that once they have served their purpose, the energy released disperses accordingly throughout its immediate environment while the resulting shell of the former charged particle attracts to and integrates with other forms of matter.
"Void"
The third byproduct is the uncharged anti-particles, a large amount of which constitute what is called "void." The reason "void" floats is because it repels every other particle except for charged spellfire particles. As a result, "void" rises up, seeking equilibrium above the atmosphere, where there is no air pressure, as there is no matter to repel there.
This had been considered a waste product until engineers in Combria in the late 1000s, early 1100s, found a method to contain it. Since then, "void" has been considered a valuable commodity, being able to provide better buoyancy than even hydrogen or helium. Thus, "void" was paramount in the development of modern airships in the centuries to come, and, since the obsoletion of airships, has served as an important component in altitude control for gyroplanes.