This is the largest tern, with a wingspan longer than that of the common gull. The beak of the adult is very stout and bright red; most have a dark spot on front of the tip, while the primary feathers are dark in all plumages. The legs are black with a dark head and a face mask.
The common tern is very similar to the Arctic tern. The common tern has a longer beak, legs, head and neck and slightly bigger wings. In summer, the beak is orange-red with a black tip, the underside is a pale grey with little to no contrast to the white cheeks, the tail feathers do not reach beyond the wing tips, the primary feathers are white below and the rear edge of the wing is widely or disjointedly darker. In winter, the forehead and underside are white, the front edge of the wing bend is dark and the beak is entirely black.
The legs and base of the beak are red, the top side is brownish, the chest is striped, the sides are spotted, there is a bright ring around the eye and short eyebrow stripe. During flight, the wide white trailing edge of the wing and the white oblong-triangular preen gland area are visible. In the summer, adult birds have thick, slightly irregular specks and streaks on both the top and undersides; however, in the winter, the top side and breast area are brownish-grey.