Actually a green onion, a scallion is an immature onion with a white base (not yet a bulb) and long green leaves. Both parts of the scallion are edible.

Jamaican scallion or escallion is immature onions young leeks and sometimes the tops of young shallots. The Jamaican vegetable has a white base that has not fully developed into a bulb and green leaves that are long and straight. Jamaican scallions can be cooked whole as a Jamaican vegetable much as you would a leek. They can also be chopped and us [..]

(SKAL-yuhn) – The name scallion applies to several members of the onion family including a distinct variety called scallion, immature onions (commonly called green onions), young leeks, and sometime [..]

Actually a green onion, a scallion is an immature onion with a white base (not yet a bulb) and long green leaves. Both parts of the scallion are edible.

(n) plant having a large slender white bulb and flat overlapping dark green leaves; used in cooking; believed derived from the wild Allium ampeloprasum(n) a young onion before the bulb has enlarged; [..]

sliced Spanish onion often used as garnish for broths or other clear soups.

late 14c., scalun "kind of onion," also "thing of little value," from Anglo-French escalone, Old North French escalogne, or Old French eschaloigne, all from Vulgar Latin *escalonia [..]