In English-speaking countries "Latte" is a name for several kinds of hot drinks made with coffee and milk. However, Latte is actually Italian for milk. In Italy coffee beverages made using hot milk are usually called "caffé e latte", or simply "cafelatte", which literary means "coffee and milk". Similar (but not identical) drinks are latte macchiato and French "café au lait".
Latte as we know it (since early 1980s) is made of one part espresso and two parts steamed milk. It is similar to cappuccino (which has one part espresso, one part steamed milk and one part milk froth), but has more milk, thus milder taste. An interesting thing in preparing lattes is that coffee and milk should be poured simultaneously, from either side of the cup.
Actually, there are three different beverages made with coffee and steamed milk; they are differed dew to milk froth over them. Flat White is a coffee beverage widely popular in Australia and New Zealand; it contains (just like a latte) one part espresso and two parts steamed milk, but has no froth over it. Common latte has about one centimeter (about 1/3 of an inch) froth making a latte art. In cappuccino froth fills up about one third of the cup.
Latte is a rather "young" beverage. It was introduced in its current form and with its current name somewhere in 1980s along with Seattle's Starbucks development. Earlier in an Italian coffeehouse you would probably get a glass of milk instead of a "latte" as we know it if requested one. And even for a "caffélatte" the drink would contain much less milk than it is expected to contain today.
There are several tips and hints to latte preparation. For example, some baristas heat milk only to 65-70 °C (150-155 °F) claiming that above that temperature the milk changes its flavor. Lattes are commonly made with a shot of espresso (about 30 ml) and with twice as much of steamed milk on top. Latte can be served in a cup or a glass on a saucer with a napkin which is used to hold the drinking vessel that can be rather hot. In some establishments lattes are even served in bowls.
Nowadays hot and iced latte versions of numerous tea and coffee products are available in different establishments in Asia and North America. Indian chai, Japanese powdered green tea called matcha, and Royal milk tea are among them.