Botanically speaking, a coconut is a fibrous one-seeded drupe, also known as a dry drupe. However, when using loose definitions, the coconut can be all three: a fruit, a nut, and a seed.

It is the only accepted species in the genus Cocos.[2] The term coconut can refer to the entire coconut palm, the seed, or the fruit, which, botanically, is a drupe, not a nut. The spelling cocoanut is an archaic form of the word.[3] The term is derived from the 16th-century Portuguese and Spanish word coco meaning 'head' or 'skull', from the three indentations on the coconut shell that resemble facial features.[4]

Botanists love classification. However, classification of plants can be a complicated matter for the average person. Coconuts are classified as a fibrous one-seeded drupe. A drupe is a fruit with a hard stony covering enclosing the seed (like a peach or olive) and comes from the word drupa meaning overripe olive. A coconut, and all drupes, have three layers: the exocarp (outer layer), the mesocarp (fleshy middle layer), and the endocarp (hard, woody layer that surrounds the seed).

The coconut we buy in the store does not resemble the coconut you find growing on a coconut palm. An untouched coconut has three layers. The outermost layer, which is typically smooth with a greenish color, is called the exocarp. The next layer is the fibrous husk, or mesocarp, which ultimately surrounds the hard woody layer called the endocarp. The endocarp surrounds the seed. Generally speaking, when you buy a coconut at the supermarket the exocarp and the mesocarp are removed and what you see is the endocarp.