In Starspan, a world is any inhabited, unified distinct geographic unit not connected to any other inhabited, unified nor distinct geographic unit by natural terrain by any amount of walking. A world can be an inhabited planet, moon, asteroid, or space station. Inhabited satellites (artificial or natural) are each worlds of their own. A new, recently colonized location qualifies as a world, with the subcategory of 'colony.' As a colony grows to a certain point, it loses its 'colony' status and becomes just a normal world.
The main game interface will have a control for "Worlds" that will list each seperately. If the player's empire has Earth, the orbitting International Space Station and a colony on the moon, then the player's empire has three worlds: Earth, the I.S.S. and the Moon.