The coconut palm is a plant native to Earth that produces a simple dry fruit that is roughly circular with an extremely tough and durable exterior. This exterior has a husk on it which is normally brown in color.
Once this hard, shell-like exterior is opened, the inside of the coconut fruit yields a white, sweet, fleshy "meat" which is edible. Also inside the coconut fruit is a liquid referred to as "coconut milk."
Coconut fuits and the milk from them are used often in cooking and in the making of beverages. Geordi La Forge offered Christy Henshaw a drink called a Coco-no-no which was made from the hollowed-out half of a coconut shell, while the two were on a date on the holodeck. (TNG: "Booby Trap")