What is "eastphalia"

Eastphalia (; Eastphalian: Oostfalen) is a historical region in northern Germany, encompassing the eastern Gaue (shires) of the historic stem duchy of Saxony, roughly confined by the River Leine in the west and the Elbe and Saale in the east. The territory corresponds with the southeastern part of the present-day states of Lower Saxony, western Saxony-Anhalt and northern Thuringia. Together with Westphalia, central Angria and Nordalbingia it was one of the four main Saxon administrative regions. It should not be confused with East Westphalia (Ostwestfalen).