I think South Loop is a good descriptor from Congress to just south of Roosevelt, ending somewhere between 14th - 16th Streets. According to Google Maps though, the South Loop goes as far south as 55 (roughly 25th St), which is way excessive IMO. I refer to the area between 14th and 26th, wedged between the river and the lake, simply as the Near South Side. Don't have any other names for it, really. I'm open to anything, although I'd prefer to stay away from crappy acronyms