A seabird (family Sternidae) resembling a gull but lighter, more streamlined, and with a longer bill and tail, and long, narrow wings. Most are white or pale grey with a black cap. They occur worldwide and breed on all continents, including Antarctica, and many are long-distance migrants, the Arctic tern (Sterna paradisaea) migrating between its Arctic breeding grounds and waters around Antarctica, a journey of 15,000 km each way. There are 11 genera of about 45 species.