A scallion is a young onion you eat while the white end is still small and the green stem is long. In American English this is the everyday name; British speakers often say spring onion for the same vegetable. You slice it onto noodles, dumplings, and soup. Though actually, cooks do not all agree where scallion stops and green onion or shallot starts — shop labels mix them — but for learners, picture the long green 青蔥, not the fat round 洋蔥, and not the little pink 紅蔥頭.