The ancient vox-caster servitor coughed a plume of dust from the brass mesh that caulked its disgorged throat as the Scribitor Prime ascended the pulpit to address the supplicants. He paused, gazing over the trembling heads of the young men and women arrayed before him, then began to intone the Hymnal of Aeons, used since time immemorial to induct the new adepts to the Order or Planetary Records.

'The Imperium of Man has endured for countless centuries; weathering invasion, insurrection, heresy and disaster alike. It is made up of one million worlds, spread as thinly across the stars as the gossamer-webs of mobius-spiders.

'From mighty Fortress worlds to the pomp of Cardinal planets; from industrious Forge worlds to Orbital hive platforms, each is unique; the sole preserve of cultures and customs that will one day become naught but whispers on the sea of souls.

'Your task will be to record these thousand, thousand worlds: enshrining them in holy writ for eternity. Do not take this responsibility lightly: no one man can know the extent of the Emperor's domains. Struggle only to record faithfully those you come to know.'

This thread caught my imagination:

There are one million human-inhabited worlds to fight over – and roughly seventy million more planets in the galaxy; giving us an almost infinite variety of battlefields and background.

I thought it might be fun to collect together some one sentence descriptions of these myriad worlds to inspire some scenarios. Feel free to join in with a one sentence description of a planet or world to see if you can catch someone's imagination.

Try using canon planets if you can encapsulate them in a sentence – or why not post your army's homeworld? Imagination, creativity and succinctness are the only limits.

I'll start you off:

...from the dust-fields of agri-world Joh, where labourers sweat for nine hours a day, twelve days a week – and spend the rest of their time frantically cleaning their oculars, praying and catching a precious few hours of tortured sleep...