Green onions are also called scallions.
What's the Difference Between Scallions, Green Onions, and Spring Onions?
More About Scallions and Green Onions
Green onions and scallions are actually the same thing! They are either harvested very young from the regular bulb-forming onions we are familiar with, or they can come from other varieties that actually never form bulbs.
Scallions are long, with a white stem end that does not bulge out. They have an onion-y but mild bite that is not as intense as regular onions (the white parts contain the most intense flavor). They can be used raw or cooked, and while some cooks discard the darker green tops, the whole thing can be eaten, and is often used in Asian cooking.
Scallions are usually available year-round. Look for a bright color, undamaged leaves, and firm stem ends.
More About Spring Onions
Spring onions, on the other hand, look similar to scallions, but you'll notice that they have small onion bulbs at the base. These onions come from the varietals that produce bulbs and are basically more mature versions of scallions. They are planted as seedlings in the late fall and then harvested the next spring, thus the word "spring" in the name.