The term 'Scallion Cousins' refers to the two vegetables leeks and scallions. Both are members of the onion family, but they have distinct differences in flavor and texture. Leeks are milder and sweeter than scallions, and their white and light green parts are edible. Scallions, on the other hand, are more pungent and have a stronger flavor. The white part of the scallion is edible, but the dark green part is usually discarded. Both leeks and scallions are commonly used in cooking, and they can be used interchangeably in many recipes.