Downtown is a term primarily used in North America by English speakers to refer to a city's core (or center) or CBD (Central Business District), often in a geographical, commercial, or communal sense.
The term is thought to have been coined in New York City, where it was in use by the 1830s to refer to the original town at the southern tip of the island of Manhattan.[2]
During the late 19th century, the term was gradually adopted by cities across the United States and Canada to refer to the historical core of the city (which was most often the same as the commercial heart of the city).[4]
http://en.wikipedia.org/wiki/Downtown