Pyrena

A pyrena (/paɪˈriːnə/) or pyrene, commonly called a pit or stone, is the fruitstone within a drupe or drupelet produced by the ossification of the endocarp or lining of the fruit. It consists of a hard endocarp tissue surrounding one or more seeds (also called the "kernel"). The hardened endocarp which constitutes the pyrene provides a protective physical barrier around the seed, shielding it from pathogens and herbivory.

While many drupes are monopyrenous, containing only one pyrene, pome-type fruit with a hard, stony (rather than leathery) endocarp are typically polypyrenous drupes, containing multiple pyrenes.