Perle biseri parel pearl perla perla perle pärla pérola πέρλα פנינה parels pearls A smooth round bead formed primarily within the shells of two distantly related groups of molluscan bivalves or clams, including the ocean-dwelling pearl oysters and the freshwater river mussels. Pearls are used in jewelry and for other ornamental puposes; they are considered a gem (AAT).