ZOE: The border worlds -- just like the central planets, they're as close to Earth-That-Was as we could make 'em: atmosphere, gravity and such, but...
MAL: Once they're terraformed, they'll dump settlers on there with nothing but blankets and hatchets and maybe a herd. Some of them make it, some of them...
The technology of terraforming worlds is clearly not perfect, resulting in a spectrum of colonial worlds ranging from plague-infested rat holes to clearly privileged worlds with all the latest advantages of technology.
Terraforming is the process of transforming a planet's surface and atmosphere to Earth-like standards, so that human and Earth animal and plant life can live on it. Once planets are thus changed, colonists are placed on them with minimal resources and expected to develop on their own. Thus, the closer to the center of the Alliance one goes, the older the planets and higher the level of technology, and, as one might expect, the further out towards the rim you get, the younger and less developed they are.