Guarana's biological name, Paullinia cupana, was taken from the German medical botanist Christian Franz Paullini, who discovered the tribe and the plant in the 18th century.
The Guarana plant contains caffeine, and so acts as a stimulant. Like many other caffeine-containing plants, it is used for drinks; a kind of carbonated soft drink that is made from the Guarana berry is known as "Guarana". The word "Guarana", in this sense, is akin to the word "Cola". Thus, just as there are a number of Colas (Coca-Cola, Pepsi-Cola, RC Cola, etc.), there are a number of Guaranas, such as Guarana Antarctica. All these drinks are fizzy and sweet, and taste a little bit like bubble gum. Most Guarana of this sort is produced in Brazil and consumed either in Brazil or in nearby countries, such as Paraguay.
There are a number of other drinks containing the Guarana berry available for purchase worldwide. Most of them are not called Guarana, and do not taste like the Guarana drinks mentioned above.