Tea types are often easy to recognize visually and are the most common way of referring to a tea. (“What kind of tea are you drinking?” “Green.”) The major types of tea are: White, Green, Oolong, Black, and Pu-erh.
White tea is the most prized and least processed of all the tealeaves. It comes from the delicate, immature buds and/or leaves of the first flush. After harvesting, it is simply dried. Traditionally, it is left to dry in the sun. Today, some use ovens or fire, but many still follow the custom of sunning. This minimal processing retains the most antioxidants and results in the lowest caffeine level of the leaf (unpowdered) true teas. White tea has a very mild taste that can be somewhat floral. The leaves/buds are very pale/”silvery” in color and produce a pale infusion. A good white tea will have fine white “hairs” covering its surface. The white hairs often stand out on the surface of the darker leaf color due to oxidation during withering in the sun, but many people will tell you white tea is not oxidized. Because white tea is so prized, there are a lot of people making "white tea" instead of white tea. The jury is still out on the exact definition, and some are pushing for an industry standard to eliminate/reduce counterfeits.
Green tea can be produced from any flush; however, it is typically produced from the third flush in India and, in areas of China that produce a lot of white tea, from the second flush on (although prized green teas are usually from the first flush in China). Unlike white tea, the leaves may be twisted, rolled, or otherwise shaped during processing. They are also either roasted (most common in China) or steamed (most common in Japan) to dry them and stop them from oxidizing. There is a wide range of flavors and appearances with green tea plus, it tastes great.
Oolong has more processing than green tea. It is semi-oxidized. That is to say that a chemical reaction is allowed to occur before the tea is dried and the chemical reaction is halted. This reaction is encouraged by bruising of the tealeaves and multiple firings over a period of time. Oolongs range from very close to green ("pouchong" or "green oolong" teas are about 10% oxidized) to very near black (about 90% oxidized). They are capable of holding very complex, layered tastes and are excellent on their own.
Black tea is fully oxidized. The chemical reaction in it is not halted, but allowed to end on its own. After the oxidation is complete, the tea is fired to dry it and to prevent it from going bad. Black teas often have the most caffeine of true teas. Their flavor tends to be strong and earthy. Some black teas are smoked. Many black teas are flavored or served with milk and/or sugar. The color of the leaves is very dark brown to black and the color of the brew is a red-brown color. (In China and Japan, they refer to “black” tea as “red” tea for this reason. Rooibos drinkers may get very confused by this!) In the world of tea, black tea is a relative newcomer.