'They are crescentic or moon-shaped and occur individually or in groups'. The above description refers to

Answer Details

The description "They are crescentic or moon-shaped and occur individually or in groups" refers to a type of sand dune known as "barchans". Barchans are crescent-shaped dunes formed by the action of wind, which blows sand grains up the gently-sloping windward side and deposits them on the steeply-sloping lee side. They are commonly found in arid regions and can occur singly or in groups.