Slime mold is the default name for NetHack's customisable fruit. You can change it, with the fruit option, to almost anything you like. You could choose slice of pizza or bowl of gruel or leg of ham and the game will identify pizza, gruel and ham as the food part, giving messages such as "This tastes like ham juice" when quaffing certain potions. However, NetHack will prevent you from naming your fruit after a corpse or tin, or with a word indicating BUC status; if you try, you will have a candied corpse, tin, or blessed/cursed/uncursed fruit instead.
The name you choose has no impact on gameplay; the fruit will be worth 250 nutrition points (whereas melons are only 100 points each, and other fruit are less). For conduct purposes, NetHack assumes that the fruit is vegan.
If you leave a bones file with any custom fruit in it, the name will be preserved for the player who finds it. Thus it is possible to have several different pieces of customised fruit in one game.
If you change the fruit option while a slime mold exists, the slime mold remains a slime mold, and not the current fruit setting.
Slime mold or slime fungus, organism usually classified with
the fungi, but showing equal affinity to the protozoa. Slime
molds have complex life cycles with an animal-like motile
phase, in which feeding and growth occur, and a plant-like
immotile reproductive phase. The motile phase, commonly
found under rotting logs and damp leaves, consists of either
solitary amoebalike cells or a brightly colored multinucleate
mass of protoplasm called a plasmodium, which creeps about
and feeds by amoeboid movement.