This from wiki....
Botanically, a coconut is a
simple dry fruit known as a
fibrous drupe (a true
nut). The husk (
mesocarp) is composed of
fibres called
coir and there is an inner "stone" (the
endocarp). This hard endocarp (the outside of the coconut as sold in the shops of non-tropical countries) has three
germination pores that are clearly visible on the outside surface once the husk is removed. It is through one of these that the
radicle emerges when the
embryo germinates. Adhering to the inside wall of the endocarp is the
testa, with a thick albuminous
endosperm (the coconut "meat"), the white and fleshy edible part of the seed. The endosperm surrounds a hollow interior space, filled with air and often a liquid referred to as
coconut water, not to be confused with
coconut milk.
Coconut milk is made by grating the
endocarp and mixing it with (warm) water. This produces a thick, white liquid called
coconut milk that is used in much Asian cooking, for example, in curries.
Coconut water from the unripe coconut, on the other hand, is drunk fresh as a refreshing drink.
When viewed on end, the endocarp and germination pores gives to the fruit the appearance of a
coco (also Côca), a
Portuguese word for a scary witch from the
Portuguese folklore, that used to be represented as a carved vegetable lantern, hence the name of the fruit
[1]. The specific name
nucifera is Latin for
nut bearing.
When the coconut is still green, the endosperm inside is thin and tender, a favourite snack. But the main reason to pick the nut at that stage is to drink its water; a big nut contains up to one litre of refreshing drink. When the nut has ripened and the outer husk has turned brown, a couple of months later, it will fall from the palm of its own accord. At that time the endosperm has thickened and hardened, while the coconut water has become somewhat bitter.

Coconut flower. Location:
Taliparamba,
Kannur,
Kerala,
India.
To open a coconut, remove the outer husk (if not purchased already removed) and pierce two of the three
eyes of the fruit (one for the juice to come out of, one to enable air to go in); drain the
juice from the fruit. Since coconuts have a naturally-forming fracture point, they can be opened by taking a heavy knife, such as a meat cleaver, and striking the coconut with the flat edge of the knife. Or you can use a flat-bladed screwdriver and a hammer (which is easier, and may be safer than using a cleaver). After inserting the screwdriver slightly, twist it to crack the shell. The coconut should then be turned, and this process repeated until there is a contiguous crack in the shell around the entire fruit. Afterwards, the fruit can be separated at this fracture point.
More here:
http://en.wikipedia.org/wiki/Coconut