Black tea is tea made of oxidized tea leaves. It is stronger than less oxidized teas such as green tea, white tea, and oolong. As with green, white, and oolong teas black tea comes from the small Camellia sinensis shrub. Among this species two principal varieties are used: the small Chinese variety of plant (C. sinensis subsp. sinensis), which is used for most non-black teas, and the large-leaved Assamese plant (C. sinensis subsp. assamica), which is predominantly used for black teas.
In Chinese, and in many neighboring countries, this type of tea is referred to as "red tea," a description of the color of tea water; "black tea" in Chinese typically refers to post-fermented teas, such as Pu-erh tea. In Western countries, "black tea" typically refers to the color of the oxidized leaves.
Unlike green tea which loses its flavor in less than a year, black tea retains its flavor for several years and as such has long been used in trade and had even been used as currency. Black tea is the most widely sold tea in the World accounting for over 90% of all tea sold.
Unblended black tea varieties are typically named after the region in which they are grown. Commonly recognized black teas include Ceylon, Darjeeling, and Assam. Black tea is often blended with other plants or oil to create a tasty beverage. For example, black tea is combined with bergamot oil to create Earl Grey.