User blog comment:StormWarriors2/The Widow Systems/@comment-24909831-20150128162551/@comment-24909831-20150129161848

Subsector, usually for at least, consist of handfull of systems. Or in appropriate cases of a single system (and possible nearby space stations, guard outposts, naval bases) that is extremely valuable and important in sense of Warp routes. You could think sub-sector as duchy, if particular county is important enough, it might gain duchy status to improve taxation and in 41st millennium, fleets, guard regiments, presence of Adepts et cetera. Worlds ripe with crime and rebellions aren't such places, I'd say for the least.

I'd say, that a Hive World has an actual Hive city on it. Hosting +50 billion inhabitants for the very least. I think that any world with over 10 billion inhabitants is considered as Hive world in some older edition's fluff, but I'd go for the actual hive city. We could call a planet of 10-50 billion inhabitants as proto-hive world, if we'd like to. I think that smallest (in a matter of population) hive world in fluff has 80 billion inhabitants, when the biggest have over 180 billion making them great sources of manpower for Imperium.

When we are talking about frontier sectors of Ghoul stars, I wouldn't go for a hive world, because it takes some time to develope into such world anyhow. As I've understood, Ghoul Stars area is pretty sparsely populated area.