红豆沙 is a sweet paste made from cooked and mashed red beans, also known as adzuki beans. It is commonly used in various Asian desserts, providing a rich, slightly sweet flavor. The paste can be found in items like mochi, mooncakes, and buns, making it a popular ingredient in traditional sweets. This delicacy is not only enjoyed in China but also in other countries, including Japan and Korea, where it is often referred to as anko or pat. 红豆沙 can be served warm or cold, and it is sometimes used as a filling or topping for desserts, enhancing their taste and texture.