1 : (count) US : a meal to which everyone who is invited brings food to share
He organized a neighborhood potluck for next Saturday.
– often used before another noun
a potluck dinner/supper
2 : (noncount) chiefly British : a meal for a guest that is prepared from whatever is available
I wasn’t expecting you for dinner, so you’ll have to take pot luck.
– often used figuratively
We don’t have definite plans. We’re just going to take pot luck. (=we’re just going to take/accept whatever is available and hope that it is good)