Orkiformed world
What happens when a Waaagh leaves a planet? You leave behind Feral Orks, but what happens to a planet that has been completely lost to the Orks? What happens when the Ork fungus has infested a planet so far from beyond recovery that even nuking the planet from orbit wont get rode of it?
Well you're looking at an Orkiformed World.
Orkiformed worlds are planets that have been under Ork control for so long that literally the only lifeforms still around are orkoid in nature; every tree has been cut down and replaced with a mushroom, every animal has been hunted to extinction and replaced with a form of Squig, there is no more intelligent life left apart from the Orks, Gretchin and Humans who think they're orks but are treated like Gretchin.
Orkiformed worlds are usually located in the centres of Ork empires since otherwise the imperium would immediately call for an exterminatus.
One of the most famous examples of an Orkiformed world has to be from The Beast where they mention that the orks had managed to industrialise skinning and eating humans, breeding them like cattle while forcing other humans to be their prison guards; how exactly this planet remained undiscovered for so long since they mentioned it wasn't in a previously formed Ork empire remains unknown, but chances are they simply painted the entire planet purple.