For many years we have referred to all hot beverages, other than coffee or hot chocolate, as tea regardless to what is actually in them.
Tea; green, black, oolong, white and pu'erh, come from one plant camellia sinensus. While different from one another all of these are "tea" in the true sense of the word. It is the processing of the leaves that makes them differ from each other.
On the other hand herbs like peppermint, lemon grass and valerian come from a variety of plants, none of which are camellia sinensus. The herb category would also include dried flowers such as chamomile, lavender and hibiscus.
Also include in the herb category is Rooibos. Found only in South Africa Rooibos is naturally free of caffeine and has a variety of properties considered good for you.
Tea is grown in countries around the globe. The largest producers of tea are China and India which produce more than half of the world's teas. Teas are also produced in Sri Lanka, Kenya, Japan, Indonesia, Viet Nam and several other nations.
Most of tea growing regions specialize in particular tea types: Japan is known for its green teas while Taiwan is famous for its oolongs. China, on the other hand, produces all tea types including whites, greens, oolongs and blacks.