Aurorae Sinus is a dark feature in the southern hemisphere of the planet Mars. Together with albedo features contributed by Aonius Sinus and Solis Lacus, it is part of a feature known as the "eye of Mars". (wikipedia entry)
A albedo feature is an area which shows a contrast in brightness or darkness (albedo) with adjacent areas. On Mars they are named after names from classical mythology assigned by Schiaparelli and Antoniadi.