It is distinct from Ostfriesland – also translated to English as "East Frisia" – which refers to a historic region that occupies the western half of the peninsula (Aurich, Leer, Wittmund and Emden).
Ostfriesland covers the territory of the former County of East Frisia, which roughly corresponds to the present-day districts (Landkreise) of Aurich, Leer and Wittmund and the town of Emden.
By contrast, Ost-Friesland includes, as a rule, the other traditionally Frisian parts of the peninsula: the town of Wilhelmshaven and the Oldenburg district of Friesland (Jeverland and Friesische Wehde).
The publishing house of Brune-Mettcker from Wittmund uses the term Ost-Friesland for the circulation area of its three daily papers, which cover eastern East Frisia, the northern part of Friesland district and the town of Wilhelmshaven.
[1] In its broadest definition, Ost-Friesland can be used to embrace all the Frisian parts of the German state of Lower Saxony, i.e. those areas which represent the "East Section" of the Interfrisian Council (which include the former Rüstringen (Butjadingen etc.
In spoken German, to emphasise that Ost-Friesland is meant and not Ostfriesland, the stress is placed on the prefix Ost instead of on the syllable fries.