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).
Northern Germany
In the Early Middle Ages, Northern Germany was the settlement area of the Saxon tribes, which were subjugated by the Frankish ruler Charlemagne in the Saxon Wars from 772 onwards, whereafter the Imperial Duchy of Saxony was established in 804. In the 10th century the Saxon lands, enlarged by the Saxon Eastern March, became the cradle of the Kingdom of Germany and the Holy Roman Empire, when the dukes of the Ottonian dynasty were elected King of the Romans and crowned Holy Roman Emperors.