Arcosians are a race presumably belonging to the Frieza Force. They were named only in the original Funimation dub of Dragon Ball Z.
Their appearance has them wearing white cloaks and what resembles gas masks, as well as apparently being green.
They are most notably responsible for supplying the Saiyans with Battle Armors and other technology. In return for this technology, the Saiyans would conquer planets for the Arcosians.