Ridges or moulds of loose, wind blown sand (fine to medium) forming on the backshore and forming the coastal features at certain locations. Dunes are more or less vegetated. Dunes are active coastal form elements acting as a flexible sand reservoir.
Definitions of Dune - Further information
At eroding coasts dunes are moving backwards in parallel with the erosion process. Dunes act as a kind of flexible natural protection against erosion and flooding. If the vegetation is damaged by too much traffic or grazing etc. the integrity of the dunes may be endangered.
The coastal sand dunes of Europe are one of the main categories in the Coastal Wikipedia forming one of the main coastal terestrial habitats. There is also an extensive literature in the Wikipedia .