TeanKC

In the tea industry, tea is defined as the dried processed leaves of Camellia sinensis, or Thea sinesis. Commercially, there are three major varieties of Camellia sinensis: the China type, the India (Assam region) type, and the Hybrid type (a cross breed of the China and India types). The China type tea plant has small leaves and usually grows well at higher altitudes. The India or Assam type has larger leaves and cultivates best at lower elevations. The Hybrid falls somewhere in between the China and India types.
There are four major types of tea: White, Green, Oolong and Black. Interestingly, all these teas come from the raw leaves
of the same tea plant, Camellia sinensis. What distinguishes each category is the method used when processing the tea leaves. The way the leaves are processed-steamed, fermented (oxidized), dried, or bruised-gives the tea the special characteristics of its category.

Excerpt taken from planet-tea.com

Tea is an infusion(water or oil in which plants have been steeped) made by steeping(soaking) processed leaves, or parts thereof of the tea bush, in hot water for a few minutes. The processing of these tea leaves, stems and/or twigs can include oxidation, heating, drying and the addition of other items such as herbs fruits, flowers or spices.  The four basic types of “true tea” are (in order from most to least processed): black, oolong, green and white. The term “Herbal tea” generally refers to infusions of anything other than tea leaves, usually fruit or herbs.