A tombolo is a sandy or shingle isthmus. A tombolo, from the Italian tombolo, meaning 'pillow' or 'cushion', and sometimes translated incorrectly as ayre (an ayre is a shingle beach of any kind), is a deposition landform by which an island becomes attached to the mainland by a narrow piece of land such as a spit or bar. Once attached, the island is then known as a tied island. Several islands tied together by bars which rise above the water level are called a tombolo cluster. Two or more tombolos may form an enclosure (called a lagoon) that can eventually fill with sediment.