The Nine are a faction or race that live in the outer planets, probably Jupiter, and Saturn. The pyramid shaped ships we seen in the concept arts, this is them. They probably live in these ships. Orbiting the gas giants and possibly inhabiting the moons of these planets. The Nine and the awoken of the reef kinda have a thing. Weather or not they are allies.. I'm not sure. But in the lore, Uldren sent one of his mechanical crows to spy on them. The nine found out and as an apology gift the Queen sent the body of a HoW nobility (Not dead but stripped of its soul. The prison of elders is like a trophy room with body's with detached souls). Now about xûr, he's openly stated he is part of the nine. And he's being sent the perhaps as an emissary similar to the queens. Xûr is represented of what the the nine are like. Under his hood it looks like he has a shadowy head, like gas maybe. Or it may just be artificial to hide his identity. But that is what the nine are like. Then they are either) . A race that choose to embrace the darkness, ( similar to the hive which alters their appearance) .They are a completely different race that sought out the universe. Finally this brings us to there name, The Nine. What exactly does it mean? There are 8 planets in our solar system the 9th is not even a planet but a dwarf planet, Pluto. It's possibly the nine have originated from Pluto? So what are your ideas about the nine?