Black tea comes from the leaves of the camellia sinensis plant that have been processed in a certain way. It is one of 4 types of teas, the others being white, green and oolong.
Black tea processing requires a full oxidation of the leaves. That is, the leaves are processed so as to expose the enzymes in the leaves to oxygen. Once the leaves have been dried for 8-24 hours, the leaves are rolled to begin the oxidation process. It is this oxidation that turns the leaves to a deep black color.
The leaves are dried for a final time, then sorted, graded and packaged.
Black teas can come from China, India and Sri Lanka.