This dance is called Authentic Jazz because it grew concurrently with early jazz music. Used loosely the term describes all styles that were invented to accompany jazz music, including partnered styles, but nowadays it is used to describe the purely solo dance styles that grew in the 1920s and 30s.
A number of classic routines have survived the decades more or less intact, but authentic jazz is simply a repertoire of steps, derived mainly from tap, African dance, Charleston, and earlier partnered swing styles such as Breakaway. New steps have been invented since that time, retaining the vintage styling to differentiate them from modern jazz dance.
Authentic jazz is a lot of fun, and very expressive – you can let loose without worrying about a partner! It is also great for your partnered dancing as it improves rhythm, musicality, styling and understanding of jazz structure. There are also a lot of steps which can be incorporated into your partnered swing dance and are easily led and followed.