A structure, often concrete or stone, built along a portion of a coast to prevent erosion and other damage by wave action. Often it retains earth against its shoreward face.

• A structure separating land and water areas to alleviate the risk of flooding by the sea. Generally shore-parallel, although some reclamation seawalls may include lenghts that are nromal or oblique to the (original) shoreline.
• A vertical or near-vertical type of shoreline armouring characterised by a smooth surface.