The short answer
South End is a district of Charlotte, North Carolina, immediately southwest of Uptown, organized along the former rail corridor that now carries the LYNX Blue Line light rail and the Charlotte Rail Trail. Most of it falls within the 28203 ZIP code.
It is not a separate town, not part of Uptown, and not the same as Dilworth. It is a named district within the city, with boundaries that are widely understood in general terms and debated at the edges. Descriptions here are approximate; for official boundary and planning geography, consult the city's planning resources and the county's parcel viewer.
