Coca is a plant. it is used in the production of cocaine an illicit drug. It is ground up, mixed with water and then the paste laid out on a tray to dry in the sun. It then turns into a hard powdery...
The 'coca' comes from the coca plant they used in making the syrup of coca cola, incedentally the same plant used to make cocaine. The 'cola' comes from the bitter kola nuts also used in making it.