A Yiddish term, meaning "neither meat nor dairy." In Jewish dietary law (Kashrut), meat and dairy may not be eaten together, so it's important to know what's what. Some things, of course, like fruit and vegetables and water and bread (so long as it isn't made with milk) and such, are neither one, and can be eaten with anything.

Occasionally used metaphorically, with an extended meaning, as in "on that stretch of road, there's one lane going one direction, one lane for the other direction, and a lane in the middle that's sort of pareve" (presumably the left-turn lane). Compare the English "neither fish nor fowl."