Dunes are hills of sand formed by the wind, often found in deserts and along coastlines. They can vary in size and shape, depending on factors like wind direction and vegetation. Dunes play a crucial role in protecting coastal areas from erosion and serve as habitats for various plants and animals. There are different types of dunes, including barchan, transverse, and longitudinal dunes. Each type has unique characteristics based on how the sand is deposited and shaped by the wind. Dunes are important for studying ecosystems and understanding climate change impacts on landscapes.