A pearl is a hard, rounded object produced within the soft tissue (specifically the mantle) of a living shelled mollusk. The finest quality pearls have been highly valued as gemstones and objects of beauty for many centuries, and the word pearl has become a metaphor for something rare, fine, and admirable.

The difference between natural and cultured pearls focuses on whether the pearl was created spontaneously by nature, without human intervention, or with human aid. Pearls are formed inside the shell of certain bivalve mollusks. As a response to an irritant inside its shell, the mollusk creates a pearl to seal off the irritation.

The value of the pearls in jewelry is determined by a combination of the luster, color, size, lack of surface flaw and symmetry that are appropriate for the type of pearl under consideration. Among those attributes, luster is the most important differentiator of pearl quality according to jewelers. All factors being equal, however, the larger the pearl the more valuable it is. Large, perfectly round pearls are rare and highly valued. Teardrop-shaped pearls are often used in pendants.