What is Dust?

Dust is a by-product of the pure Unobtanium used by the ship's engines which ends up circulating in the atmosphere as rematerialised tiny particles. It is recovered by the Arch. Dust is described as a safe, low-energy isotope of Unobtanium, and is produced in an identical form by the engines of all species. So the Dust produced by one species can be converted by another species into fuel for their own needs.

Also a Currency

Dust is one of the main in-game currencies; in fact, its flexibility and wide variety of uses in crafting has made it the natural currency of the galaxy.

We know that Ship of Heroes is going to have an Auction House in Apotheosis City; the building already existed when the first SoH Youtube video was posted by Heroic Games, though there was nothing actually in the building at the time. Dust will eventually be used there as a local currency between players, as well as for NPCs selling items or services.