Meat Moss: A characteristic of the esseli homeworld, and more specifically their cities, starships, and other facilities.
See, the esseli are biotech wizards and use it for just about everything they can – although there are many things for which it doesn’t work so well, which is why their ships are cyborgs – a rich, meaty center inside a nice, solid neosteel hull and regular mechanical fusion torch. As such, most of their machinery, their buildings, etc., are essentially organs of one kind or another. (Or several kinds. Check out the heart-valve door in the pic, for example.)
The meat moss, unlike the trope suggests for most of it, does have a purpose, though. It’s the large-scale biotech equivalent of utility tunnels, taking care of distributing raw and processed materials to organs that need them, removing waste, and passing command-and-control signals around – which is to say, it’s a giant plug-in circulatory system and nervous system – complete with interface nodes both sensory and plug-your-exposed-nerve-organ-in-here – laid out on the ground and wrapped in skin.
(As for how it sustains itself? The volatile-digestion organs for ice asteroids and the odd carbonaceous chondrite are over there , the photosynthetic layers are over here, and that odd-looking wind tower yonder is a lung the size of the Empire State building.)