Off shore bar is a long narrow ridge of deposited materials sand can be found lying away from and parallel to a coast.
When the waves approach a gently sloping coast , friction between the waves and the sea bed causes the waves to break at some distance from the coast.
Over time, more materials are built up parallel to the coast to form ridge of sand called offshore bar.
A body of coastal water may be partially or completely cut off from the open sea by the offshore bar. The body of water is called a lagoon.