A sand dune is a hill or ridge of sand that is formed by the wind. These natural formations are commonly found in deserts and along coastlines. Sand dunes can vary in size and shape, depending on factors like wind direction and the availability of sand. They play a crucial role in protecting coastal areas from erosion and serve as habitats for various plants and animals. Sand dunes are often classified into different types, such as barchan, transverse, and longitudinal dunes. Each type has unique characteristics based on their formation processes. Dunes can also shift over time due to changing wind patterns, making them dynamic landscapes that are constantly evolving.