Camellia sinensis a famous Asia tea (Chinese, Vietnam and Japan)

 Tea (Chinese 茶) is a beverage made from the tea plant, Camellia sinensis. 

Camellia sinensis, the tea plant, is a species of evergreen shrub native to Asia. It is a popular beverage throughout the world and is the most widely consumed plant in the world. The tea plant has been cultivated in China for about 3,000 years. Teas made from the leaves of the tea plant are called teas.

Camellia sinensis

Tea is usually classified based on how it is processed, which loosely corresponds to its level of oxidation--a process that darkens the tea and changes the color. Fully oxidized tea is called black tea, and unoxidized tea is called green tea (white tea is also mostly unoxidized). Oolong tea is a partially-oxidized tea that is often also roasted. Another class of tea, Pu-erh, is usually considered as a category of its own. Oxidation is sometimes called "fermentation", and black tea is described as "fermented", but this is misleading as there is no proper fermentation process happening as with vinegar or alcoholic drinks.

Tea is usually classified based on how it is processed, which loosely corresponds to its level of oxidation--a process 

Most tea is made primarily out of leaves and leaf buds, although some teas are made out of only mature leaves and others are made only out of buds. A few teas, such as Kukicha, are made from twigs and stems, and some teas include a few bits of stem as well. Tea is also a flowering plant, and rarely, tea flowers are used to make a tea.

When the word "tea" is used by itself it usually refers to the tea plant. However, the word "tea" is also used together with other terms to describe other drinks made from steeping other plants in water. Teas that do not come from the Camellia sinsensis plant are usually referred to as "herbal teas", "herb teas", or "tisanes".

in most parts of the world, nearly all tea consumed and produced was black tea

Traditionally, in most parts of the world, nearly all tea consumed and produced was black tea. Outside of Southeast Asia, the term tea is often assumed to mean black tea.

In China, green tea (C: 绿茶; P: lǜchá; W: luhk-cha) is popular and consumed daily. In other parts of Asia, green tea is less common, but may be growing in popularity.

In the United States, green tea is most often thought of as a specialty drink. It is usually sold as a variety of bottled cold drinks in stores, rather than brewed at home.

 The tea industry is changing rapidly

 However, the tea industry is changing rapidly, and green, white, and oolong teas are becoming more popular both among tea drinkers in black-tea-loving countries, and tea growers in areas that historically only produced black tea are also beginning to produce more of these other styles of tea.