沙屿 (shā yǔ) is a compound noun meaning 'sand islet' — a small, low-lying island composed primarily of sand, often formed by natural sediment deposition in coastal or riverine areas. The first character 沙 (shā) means 'sand', while the second character 屿 (yǔ) means 'islet' or 'small island'; together, they describe a specific geographical feature distinguished by its sandy composition and modest size.

This term appears frequently in geographical descriptions, marine ecology reports, and travel writing about coastal regions of China, especially in the South China Sea and along the Yangtze River estuary. It is more formal and literary than everyday speech — you’ll rarely hear it in casual conversation but commonly encounter it in maps, environmental studies, or official conservation documents. Unlike generic terms like 岛 (dǎo, 'island'), 沙屿 emphasizes both scale and substrate, implying vulnerability to tides and erosion.