Posthuman worlds was the name used for planets under the control of posthumanity in the context of the Spiral Politic, the Great Houses' symbolic representation of the causal relationship between all worlds in their sphere of influenced.
Because posthumans had developed their own form of time travel, rather than being "uplifted" by contacts with either of the major powers in the War, it was difficult for the Homeworld to "chart" their worlds in the Spiral Politic, and according to The Book of the War, "many maps of occupied history feature[d] great black swathes beyond the posthuman age which might as well be marked 'here be tygers'". Their existence alarmed the Houses, who feared that the enemy may conceal some of their forces there.
Because it was the bridgehead between those parts of causality controlled by the Homeworld and the posthuman worlds themselves", Earth was not itself considered a posthuman world. Indeed, its history was surprisingly stable, considering. Siloportem was considered an example of a posthuman world, despite being a city instead of a planet, because it was "of such importance that on the map it [was] larger than many complete star-systems". (PROSE: "The Spiral Politic" [+]Part of The Book of the War, Loading...{"namedpart":"The Spiral Politic","1":"The Book of the War (novel)"})