Grey sand and dry landscape

Quick answer：

Grey sand refers to the use of grey sand in traditional Japanese gardens, which is used to represent water in the 'dry landscape' technique. Dry landscape, also known as 'kare-sansui' in Japanese, is a form of Japanese rock gardening that represents water bodies through the arrangement of rocks and white sand or gravel. It is a Zen Buddhist-inspired art that emphasizes the natural elements in a minimalistic way.