Tea is made from the tea plant Camellia sinensis. There are four major categories of tea: white, green, oolong and black. The categories refer to how much a tea is oxidized. Oxidation is the natural process that changes the color and flavor of the tea leaves. Black tea is the tea that is fully oxidized and is generally stronger in flavor than the other teas. Black tea's flavor depends on the plant varietal, season of harvest, soil, elevation, weather, cultivation and origin.