Black tea has been fully fermented during processing, and green has not been fermented at all. Oolong teas are somewhere in the middle. So what is 'white tea'?
Well, just like those other teas, white tea come from the Camellia sinensis plant. But the leaves are picked and harvested before the leaves open fully, when the buds are still covered by fine white hair. Hence the name. White tea is scarcer than the other traditional teas, and quite a bit more expensive.