In physical geography, a dune is a hill of sand built by eolian processes.
Bare dunes are subject to shifting location and size based on their interaction with the wind.
The "valley" or trough between dunes is called a slack.
A "dune field" is an area covered by extensive sand dunes.
Large dune fields are known as ergs.
Some coastal areas have one or more sets of dunes running parallel to the shoreline directly inland from the beach.
In most such cases the dunes are important in protecting the land against potential ravages by storm waves from the sea.
Although the most widely distributed dunes are those associated with coastal regions, the largest complexes of dunes are found inland in dry regions and associated with ancient lake or sea beds.