The Loop is the term used to designate the historical center of downtown Chicago. Most accurately, the term refers to an area bounded by a public transit circuit along Lake Street on the north, Wabash Avenue on the east, Van Buren Street on the south, and Wells Street on the west, but in general use it refers to the whole central business district.
Chicago's central business district, bounded on the west and north by the Chicago River, on the east by Lake Michigan, and on the south by Roosevelt Road is the second-largest in the United States, after Midtown Manhattan.
The term The Loop has different meanings. The term most explicitly applies to the area surrounded by the loop circuit formed by 'L' train tracks, and a preceding 1880s streetcar loop, but common usage defines it as the area bounded by the Chicago River on the north and west sides, Congress Parkway to the south, and Columbus Drive to the east.
In official city parlance, delineated by the University of Chicago in the 1920s, the Loop is community area of Chicago number 32, bounded by the Chicago River to the north and west, Roosevelt Road to the south, and Lake Michigan to the east, though the original boundary is strictly the area circled by the elevated CTA tracks. As the downtown area and its many high-rises expanded out past the community area over the years, "The Loop" has been used more generally to denote the entire downtown.