Definitions
1.NounAn officially set line along a shoreline, usually outside of the dry land, to demark a territory allowable to be treated as dry land, to separate the jurisdictions of dry land and water authorities, for construction and riparian activities, to establish limits to the allowable obstructions to navigation, etc.
2.NounA line in a navigable waterway established by the U.S. Army Corps of Engineers, beyond which solid fill is not permitted.