A Resource Unit, normally shortened to RU, is a measurement of construction materials found throughout the Homeworld universe.
Resource units are acquired through the mining of asteroids, processing of crystals, and collection of space dust. These are carefully categorized by the Resource Collectors to avoid false mining. The raw compounds were then converted to construction materials by Phased Disassembler Arrays.
It is also defined that RUs are a measurement of mineral wealth. The Bentusi Exchange, in both Homeworld and the backstory for Homeworld: Cataclysm, exchanged technology and other services for mined resources. Though they are not used as money, they are used directly as construction and tech materials.