Botanical term for the innermost layer of a fruit's pericarp, often hard and stony (e.g., the pit of a peach).
The endocarp of a peach is hard and protects the seed.
中果皮 (mesocarp) is the middle layer of the fruit, often fleshy, while 内果皮 is the innermost layer.
Compound of 内 (nai, 'inner') + 果皮 (kahi, 'fruit skin/pericarp'). A straightforward botanical term.