“[…] Each coconut fruit contains one giant seed, which is almost entirely white with a paper thin layer of seed coat around it. The seed contains an embryo, which can grow into a new palm, and endosperm, which is a food source for the growing embryo. When the seed is first formed, the embryo is microscopic, and the endosperm fills up most of the space inside the seed. The early embryo is slightly sweet and crunchy. As the coconut starts to get larger, the endosperm becomes somewhat more gelatinous and is known as green coconut meat. When the seeds are nearly mature, the endosperm forms solid endosperm around the outer edge of the seed and liquid endosperm inside the seed – coconut meat and coconut water. A mature coconut seed will also contain some air, which helps it float in the ocean. All stages of coconuts can be eaten, and they all taste coconutty, slightly sweat and delicious. Coconuts contain a high proportion of saturated fat, unusual for a plant but much more common in butter and animal fats.
If a coconut escapes consumption by a human and floats off to a new land, it will begin to germinate. The embryo enlarges into a root and a shoot, and it escapes the hard coconut shell through structures called eyes that look like dimples on the surface of the coconut. As the embryo starts to grow, it forms a mass inside the coconut called a coconut apple. The mass is soaks up the nutrients from the endosperm and transfers those nutrients to the growing shoot and root of the embryo. The coconut apple is also edible – in fact it’s considered quite delicious, though I have unfortunately not tasted it.”
Source: What are Coconuts anyway?