means A shared meal to which each guest brings a dish, so the menu is whatever everyone collectively shows up with.

from A 16th-century English compound of 'pot' and 'luck' — literally the luck of the pot. Originally it meant the meal you'd get as an unexpected guest: not a planned feast, just whatever happened to be cooking in the pot, take it or leave it. Over time the 'luck' shifted from the host's leftovers to the gamble of a communal table, where the spread depends entirely on chance and whoever volunteered for dessert.