The List API takes any Output Lists you have already created and serves it via a static link. You can select the format of the list in the setup or append the format to the end of the URL.
Output Formats
Standard: TXT, HTML, PDF, CSV, XML, XLSX (Excel)
Developer Focused: JSON, JSON ext (includes full formatting/CSS data from the output settings)
Potential Use Case: If you have a "Live Results" output list, you can provide the JSON link to a broadcast to display live results.