From AMS Glossary
(Also called shelf ice; formerly barrier.) A thick ice formation with a fairly level surface, formed along a polar coast and in shallow bays and inlets, where it is fastened to the shore and often reaches bottom.
An ice shelf may grow hundreds of miles out to sea. It is usually an extension of land ice, and the seaward edge floats freely in deep water. The calving of an ice shelf forms tabular icebergs and ice islands.