Upper Saxony
It was particularly to distinguish the lands from 'Lower Saxony', a concept which arose later in popular usage (though never enforced) as a term for the original Saxon lands in north and west Germany (where Low German dialects had spread), in what is now the state of Lower Saxony, as well as the adjacent Westphalian region, Holstein and the western part of today's Saxony-Anhalt north of the Harz range (Eastphalia).
Saxony
The territory of the Free State of Saxony became part of the Holy Roman Empire by the 10th century, when the dukes of Saxony were also kings (or emperors) of the Holy Roman Empire, comprising the Ottonian, or Saxon, Dynasty. Around this time, the Billungs, a Saxon noble family, received extensive fields in Saxony. The emperor eventually gave them the title of dukes of Saxony. After Duke Magnus died in 1106, causing the extinction of the male line of Billungs, oversight of the duchy was given to Lothar of Supplinburg, who also became emperor for a short time.