Planets are classified by degrees of population and whether or not they do support or oppose life in general.
Other celestial bodies such Asteroid clusters or local gas clouds are classified as Zones, depending on their safety for sublight travel or the establishment of permanent installations.
Prime Worlds / Capitol Worlds are usually but not necessarily the most populated planets within a star system. They are are considered the political and coltural heart within a system. As capitol worlds they are usually the seat of government and all major institutions. While not all systems do have a prime world, those who do are sometimes (re)named after this world rather than their primary star.
The in-space equivalent is Safe Zone, these zones are free to be traveled by any licensed spacers and require no additional permits.
Secondary Worlds classify habitable planets, which host a measurable population without holding prime or capitol status. Their population varies from small settlements to bustling metropoles rivalling those on prime worlds.
There is no separate in-space equivalent, it is also classified as Safe Zone with the same requirements.
Tertiary Worlds classify planets that are mostly uninhabited, but do support sentient life in some degree. These worlds usually are host to industrial faclities such as mining outposts or manufacturing plants, as well as military outposts, all of which may be located anywhere on the planet's surface or within its orbit.
The in-space equivalent is Mining Zone, these zones require dedicated permits to travel or establish permanent operations.
Off-Worlds are generally flagged as uninhabitable due to adverse conditions that impede or even threaten life, both on or off-planet. Therefore civilian and commercial travel to these off-limit planets is often prohibited for safety reasons. They may yet harbor military installations or guard posts.
The in-space equivalent is Hazard Zone, these zones are off-limits to any civilian travelers because of environmental hazards or military operations.