crescent-shaped sand dune which form in desert areas experiencing generally constant winds. The 'horns' of the crescent point downwind, having moved ahead more rapidly, where they become sheltered and stable. Sand moves up the windward side and collapses down the leeward side which is steeper. This net movement of sand from the windward to the leeward side causes the dune to move forwards.
Geography Dictionary & Glossary for Students \\ ITS Tutorial School (ITS) - Hong Kong.