Although the name suggests that a coconut is a nut, it is in fact botanically classified as a fruit. Specifically, a coconut is a drupe, a kind of fruit which is characterized by a fleshy outer layer and the fact that it develops from the ovary wall of a flower. Some other examples of drupes include nectarines, pistachios, almonds, and mangoes. The evolutionary advantage for drupes is that their fleshy outer layers attract animals, ensuring that they will be widely distributed along with a little natural fertilizer in the form of animal dung. In fact, some drupes are specifically designed to go through the intestinal tracts of animals.

The outer layer of a coconut is known as the mesocarp. Coconuts in the store are usually stripped of their mesocarps, but if you have a chance to see a coconut in nature, you will see the thick fibers which cover the fruit. These fibers are known as coir, and they are used in rope making and textiles in some regions of the tropics. Coir fiber is very strong and durable, although it can also be a bit itchy.

The next layer of the coconut is the endocarp, which is the hard hull of the fruit which most people see when they buy whole coconuts at market. The endocarp protects the tender fleshy endosperm, the meat of the coconut. You may also note that a coconut has several soft depressions, which are designed to allow the embryo to grow if a coconut is fertilized and allowed to mature.

People eat coconut meat because it is the only palatable part of the coconut. Coconuts are rich in fat and nutrition because the endosperm is designed to nourish the embryo as it matures, giving it a start in life until it gets large enough to start photosynthesizing and absorbing its own nutrients. The more mature a coconut is, the firmer and denser the flesh will be; in young coconuts, the meat can be almost like a jelly in texture.

Coconuts are one of a number of foods that are misnamed, at least from the view of botanists. Coconuts were probably associated with nuts, rather than fruit, because of their meat, which is intensely rich and flavorful, much like the meat of a nut. In fact, the endosperm of drupes like peaches and nectarines is also very rich, but humans cannot eat it because it is too hard, and because it contains compounds which can make people sick.