Terns are seabirds in the family Laridae, subfamily Sterninae, that have a worldwide distribution and are normally found near the sea, rivers, or wetlands. They are slender, lightly built birds with long, forked tails, narrow wings, long bills, and relatively short legs. The word "stearn" was used for these birds in Old English as early as the eighth century, and appears in the poem The Seafarer, written in the ninth century or earlier. Terns have a worldwide distribution, breeding on all continents, including Antarctica.

Source: Wikipedia