A "mother-of-pearl tray" is a tray made from mother-of-pearl, which is the iridescent inner layer of certain mollusk shells, such as oysters and abalones. Mother-of-pearl has a beautiful sheen and coloration, making it a popular material for decorative items like trays, jewelry, and inlays. Mother-of-pearl trays are often used for serving purposes or as elegant home décor pieces due to their exquisite appearance and luxurious feel. They can be found in various shapes, sizes, and designs to suit different tastes and preferences.