Glun was a cursed orcish hardbread, baked by Orcish warlocks and sorcerors. Hard and grey, it was tasteless for the most part, and apparently was mostly rind and crust. It also evidently provided an adequate environment for the growth of maggots, as described by lamenting Orcs. The only nutritional value it had was to fill the belly at all, as it lent no strenth to muscle and sinew, and it wreaked havoc on the digestion, especially amongst non-Orcs. It was nevertheless seen by some spectators as the corrupt Orcish equivalent to Elven Lembas, though that possessed not only a superior taste, but greater physical effects, than the Orc-bread.
Speculations[]
Orc-bread may in fact have been comparable to real-life hardtack, such as was baked by American soldiers in the Civil War of that land. It seems to have been designed to represent the worst ration imaginable.