Many people, after facing the array of choices for tea consumption, ask for a regular tea. After only a few months working at a tea shop, I've learned that they usually mean what is referred to as Black Tea, the stronger, darker tasting branch of the tea family. Often the staple of many western cultures' diet, Black tea's label of 'normal' stems more from necessity than taste.
Most tea consumed in China is green, and has been for the last 2,000 years. But when western explorers were introduced to tea, they faced a problem concerning spoilage. Green tea (to say nothing of the more delicate white tea) had a hard time making the long trip from China to Europe, which often took the better part of a year as the route snaked past India and Africa. It was soon discovered that Black Tea, since it had been the most processed, was most able to survive the trip. Fortunately, Black tea was quite tasty to the European palate, especially to the British who would suddenly find a strong desire to expand their empire further east.
Today, the most common form of Black tea comes in tiny bags, which was brought into wide use by Sir Thomas Lipton. Yes, THAT Sir Thomas Lipton. As it happened, Lipton's start in the tea business came when he bought large tracts of land in Sri Lanka, made fallow due to a fungal disease that ruined the coffee production in the region. He then turned around and grew tea, processing it as Black tea. To this day, most black tea either comes from Sri Lanka (often referred to the archaic Ceylon when talking about tea) or India, where the region is used to name the tea. Assam Black tea, for example, is noted for being the strongest of the black teas in terms of taste. Darjeeling tea is acknowledged for being the best quality black tea.
Other common black teas that one may come in contact with is the Earl Gray, which is black tea flavored with bergamot oil. This gives the tea a distinct citrus taste that works well as an afternoon tea. On that note, the ever-popular English Breakfast is a blend of several Ceylon and Indian teas that earned it's name from American tea sellers describing what is simply referred to as 'tea' in England.
In terms of health, black tea has the least amount of antioxidants of tea due to the extensive oxidation process that is involved with black tea production. This process also gives black tea the highest amount of caffeine: A whole 30% of what a cup of coffee would have. Much like coffee, black tea is often available in decaf, bringing it to roughly 1-2%, the same as decaffeinated coffee.