While adding a considerable amount of radiation, it restores one of the highest amounts of Hit Points out of all of the food items. According to Kai, it mostly consists of trog meat mixed with the irradiated water from the three rivers in The Pitt. This means that consuming the slop is cannibalism, as trogs are former humans that have succumbed to the environmental conditions in The Pitt. Upon serving slop, Kai will also comment, "It's your funeral."
It uses the Pip-Boy icon and world model of noodles.
Due to its extreme radiation, it would take a mere 40 servings of slop to kill you (at near zero radiation resistance).
Kai is the only source of slop in the game. If you are a collector of rare/unique items, acquire at least one 'slop' before completing the quest Unsafe Working Conditions and talking to Midea about fighting in the hole, as she will no longer serve you after Ashur's speech.
Despite the fact that eating slop is cannibalistic, it is not affected by or related to the Cannibal perk.