Maté, or Yerba maté, isn't tea. It's an infusion of leaves from a species of holly, Ilex paraguariensis. This plant is totally unrelated to the normal tea plant (Camellia sinensis). The tree belongs to the family Aquifoliaceae and grows between the 10° and 30° parallel in the Paraná and Paraguay rivers basins in South America. It is a tropical or subtropical plant, needing high temperatures, high humidity and up to 1500 mm of annual rain.

Maté is usually associated with the gauchos of the South American pampas, but is popular all over the Southern part of Latin America . The Guarani and Quechua peoples of the region have been drinking infusions of yerba mate since pre-Columbian times. According to their traditions, it is the gift of a benevolent god. In Brazil mate is called Chimarrão or cimarron.

The name "Mate" derives from the Quechua word "matí" that names the gourd (Lagenaria vulgaris) that is traditionally used to drink the infusion, see below.

(Source)

Maté-drinkers pile the leaves against the side of a round vessel (often a gourd) and pour boiling water into the remaining void. The maté is drunk through a straw with a spoon-shaped filter at the bottom called a bombilla. Maté-drinking is a social event in which gourd and straw are passed between friends.

Example of maté vessel and bombilla (Source)

It has been claimed that mate contains a special compound, ‘mateine', which resembles caffeine, but without the addicting effects. Mateine was claimed to be a stereoisomer of caffeine and thus a different substance. However, this is impossible as caffeine has no stereoisomers. Mateine thus is a synonym for caffeine. Maté may contain about as much caffein in the leaves as there is in coffee beans. Due to the way of preparation, a final cup of mate generally contains less caffein as a cup of coffee. Maté also contains two other xanthines (caffeine-like compounds): theobromine (like in cocoa beans) and theophylline (like in normal tea) that have caffeine-like effects.

Although a lot of health claims are attributed to maté, only very little has been proven. It has been proven that maté has strong anti-oxidant capacity and may reduce some effects of oxidative stress in the body.