The common name scallion is associated with various members of the genus Allium that lack a fully-developed bulb. They tend to be milder tasting than other onions and are typically used raw in salads in western cookery. Diced scallions are often used in soup, noodle, seafood, and sauce in eastern dishes.

The species most commonly associated with the name is the Welsh onion, Allium fistulosum. Scallion is sometimes used for Allium ascalonicum, better known as the shallot. The words "scallion" and "shallot" are related and can be traced back to the Greek askolonion as described by the Greek writer Theophrastus; this name, in turn, seems to originate from the Philistine town of Ascalon (modern-day Ashkelon in Israel). The shallots themselves apparently came from farther east.

Scallions are also sometimes known as green onions in the United States. Confusingly, the term "green onion" can also be used for immature specimens of the ordinary onion Allium cepa. In Great Britain and some Commonwealth countries they are called spring onions. In Wales, they may also be referred to as 'gibbons'. In parts of Australia they are known as either 'eschallots', 'shallots', or 'spring onions' depending on the region. In parts of Scotland, they may be referred to as 'Cibies'. However, in Ireland the term 'scallions' is used, while there is a variant in Jamaica that is spelled 'escallion', although the "e" at the beginning of the word is silent.