The freespacer race is effectively an anarchist commune. The Deoradh have a fierce hatred against political control, hierarchy, or dominance of any sort, so try to build their society to fit such an ideology. Instead of relying on traditional political systems, the race is thus divided into individual communes known as 'Fleets.' These are in essence mobile and self-sufficient city-states; Composed of thousands of individuals, each commune contains its own food production, material harvesting equipment, industry, and so on.
The purpose of these fleets is to search and mine new ice deposits, missions which last decades at a time (hence the need for self-sufficiency). These missions are vital to the survival of the Deoradh, since they do not have a habitable planet and they cannot synthesis water in bulk. This need of new water supplies makes their nomadic life, and therefore the existence of fleets, necessary to the survival of the species.
Each fleet revolves entirely around its respective the Mothership. The Motherships are effectively massive city-ships or carriers, and are the lifeblood of the nomadic lifestyle. They contain the mass quantities of hydroponics bays to feed the people its Fleet and the ore smelting and assembly lines to produce and maintain the ships of its Fleet. Due to their incredible mass and slow speeds, they rely on their fleets of mining and survey vessels to be their eyes and hands, so to speak. Together they eliminate the need for traditional supply lines, which would be all but impossible to maintain with the years of travel needed and the ever-changing locations of the fleets. In a manner of speaking, Motherships are rogue islands on the sea of the galaxy.
These vessels receive their names from their most symbolic role: The Mothership contains the primary Genebanks 1), cloning vats, nurseries, and other specialized facilities needed to produce children. They contained the specialized environments needed to raise Deoradh offspring safely, as in their early ages the 'natural' toxic habitat can result in high mortality among infants. Since they are responsible for the production of the populace of the entire Fleet, they are quite literally the Mother of their community, hence its name.