Question: What is the name of this unofficial, historical designation for the German state, in which the Frontier March of Posen-West was a province of the Free State of Prussia?

Context paragraphs:
Free State of Prussia: The Free State of Prussia (German: "Freistaat Preußen" ) was a German state formed after the abolition of the Kingdom of Prussia in the aftermath of the First World War.  It was the major state of the German Reich during the time of the Weimar Republic, comprising almost ⁄ (62.5%) of its territory and population. " Free state" is another German term for "republic" that was coined in contrast to the Latin word, which was associated with the enemy France in the minds of many Germans of that time.

Prussia (region): Prussia (Old Prussian: "Prūsa", German: "Preußen" , Lithuanian: "Prūsija" , Polish: "Prusy" ) is a historical region stretching from Gdańsk Bay to the end of Curonian Spit on the southeastern coast of the Baltic Sea, and extending inland as far as Masuria.  The territory and inhabitants were described by Tacitus in Germania in AD 98, where Suebi, Goths and other Germanic people lived on both sides of the Vistula River, adjacent to Aesti (further east).  About 800–900 years later the Aesti were named Old Prussians, who since AD 997 repeatedly successfully defended against take-over attempt by the newly created Duchy of the Polans.  The territory of the Old Prussians and neighboring Couronians and Livonians was unified politically in the 1230s as the Teutonic Order State.  Prussia was politically divided in the period 1466-1772, with western Prussia under protection of the crown of Poland-Lithuania and eastern Prussia a Polish fief until 1660.  The unity of both parts of Prussia remained preserved by retaining its borders, citizenship and authonomy until western and eastern Prussia were also politically re-united under the Kingdom of Prussia.  It is famous for many lakes, as well as forests and hills.  Since the military conquest by the Soviet Army in 1945 and the expulsion of the inhabitants it divided between northern Poland (most of the Warmian-Masurian Voivodeship), Russia's Kaliningrad exclave, and southwestern Lithuania (Klaipėda Region).  The former German state of Prussia (1701–1947) derived its name from the region.

Posen-West Prussia: The Frontier March of Posen-West Prussia (German: "Grenzmark Posen-Westpreußen" , Polish: "Marchia Graniczna Poznańsko-Zachodniopruska" ) was a province of the Free State of Prussia within the German Weimar Republic.  The capital was "Schneidemühl " (present-day Piła ).  The province comprised the small western parts of the former Prussian territories of Posen and West Prussia, that remained with Germany after World War I according to the Treaty of Versailles.

Free State (province): The Free State (Afrikaans: "Vrystaat" , Sotho: "Foreistata" ; before 1995, the Orange Free State) is a province of South Africa.  Its capital is Bloemfontein, which is also South Africa's judicial capital.  Its historical origins lie in the Orange Free State Boer republic and later Orange Free State Province.  The current borders of the province date from 1994 when the Bantustans were abolished and reincorporated into South Africa.  It is also the only one of the four original provinces of South Africa not to undergo border changes, excluding the reincorporation of Bantustans.

Kreis Schwerin in Posen: Kreis Schwerin in Posen (Polish: "Powiat skwierzyński" ) was a county in Prussia, first in the southern administrative Region of Posen within the Prussian Province of Posen (till 1920), then within the Province of the Frontier March of Posen-West Prussia (till 1 October 1938) and at last as part of the administrative Region of Frankfurt within the Province of Brandenburg (till 1945).  It presently lies in the western part of Polish region of Lubuskie Voivodeship.

Weimar Republic: Weimar Republic (German: "Weimarer Republik" ] ) was an unofficial, historical designation for the German state between 1919 and 1933.  The name derives from the city of Weimar, where its constitutional assembly first took place.  The official name of the state was "Deutsches Reich"; it had remained unchanged since 1871.  In English the country was usually known simply as Germany.

List of monarchs of Prussia: The monarchs of Prussia were members of the House of Hohenzollern who were the hereditary rulers of the former German state of Prussia from its founding in 1525 as the Duchy of Prussia.  The Duchy had evolved out of the Teutonic Order, a Roman Catholic crusader state and theocracy located along the eastern coast of the Baltic Sea.  The Teutonic Knights were under the leadership of a Grand Master, the last of whom, Albert, converted to Protestantism and secularized the lands, which then became the Duchy of Prussia.  The Duchy was initially a vassal of the Kingdom of Poland, as a result of the terms of the Prussian Homage whereby Albert was granted the Duchy as part of the terms of peace following the Prussian War.  When the main line of Prussian Hohenzollerns died out in 1618, the Duchy passed to a different branch of the family, who also reigned as Electors of Brandenburg in the Holy Roman Empire.  While still nominally two different territories, Prussia under the suzerainty of Poland and Brandenburg under the suzerainty of the Holy Roman Empire, the two states are known together historiographically as Brandenburg-Prussia.  Following the Second Northern War, a series of treaties freed the Duchy of Prussia from any vassalage to any other state, making it a fully sovereign Duchy in its own right.  This complex situation (where the Hohenzollern ruler of the independent Duchy of Prussia was also a subject of the Holy Roman Emperor as Elector of Brandenburg) laid the eventual groundwork for the establishment of the Kingdom of Prussia in 1701.  For diplomatic reasons, the rulers of the state were known as the King in Prussia from 1701 to 1772; largely because they still owed fealty to the Emperor as Electors of Brandenburg, the "King in Prussia" title (as opposed to "King of Prussia") avoided offending the Emperor.  As the Prussian state grew through several wars and diplomatic moves throughout the 18th century, it became apparent that Prussia had become a Great Power that did not need to submit meekly to the Holy Roman Empire.  By 1772, the pretense was dropped, and the style "King of Prussia" was adopted.  Thus it remained until 1871, when in the aftermath of the Franco-Prussian War, the King of Prussia Wilhelm I was crowned German Emperor.  From that point forward, though the Kingdom of Prussia retained its status as a constituent state of the German Empire, all remaining Kings of Prussia also served as German Emperor, and that title took precedence.

Kreis Meseritz: Kreis Meseritz ("Landkreis Meseritz" as of 1939; Polish: "Powiat międzyrzecki" ) was a district in Prussia, first in the southern administrative Region of Posen within the Prussian Province of Posen (till 1920), then within the Province of the Frontier March of Posen-West Prussia (till 1 October 1938) and at last as part of the administrative Region of Frankfurt within the Province of Brandenburg (till 1945).  Its former territory presently lies in the eastern part of the Lubuskie Voivodeship, a region of Poland, roughly resembling the extent of the present county Powiat międzyrzecki.

West Prussia: The Province of West Prussia (German: "Provinz Westpreußen" ; Kashubian: "Zôpadné Prësë" ; Polish: "Prusy Zachodnie" ) was a province of the Kingdom of Prussia from 1773 to 1824 and again from 1878 (with the Kingdom itself being part of the German Empire from 1871); it also briefly formed part of the Weimar Republic's Free State of Prussia until 1919/20.  It was created out of the earlier Polish province of Royal Prussia following the First Partition of Poland.  In February 1920, following Germany's defeat in 1918, West Prussia was divided: the mainly Slavic-speaking central parts became the Pomeranian Voivodeship of the Second Polish Republic, also known as the Polish Corridor; the city of Danzig became the Free City of Danzig, a semi-autonomous city-state under the protection of the League of Nations; the remaining territory was retained by the Free State of Prussia/Weimar Republic, with the western parts being joined to what remained of the former Province of Posen to form the new Posen-West Prussia Province, and the eastern parts being joined to the Province of East Prussia as Regierungsbezirk West Prussia.  The territory was included within Reichsgau Danzig-West Prussia 1939–45, after which it became part of Poland.

Margravate of Meissen: The Margravate of Meissen (German: "Markgrafschaft Meißen" ), sometimes known as the March of Misnia (or Misnian March), was a medieval principality in the area of the modern German state of Saxony.  It originally was a frontier march of the Holy Roman Empire, created out of the vast "Marca Geronis" in 965.  The margravate was finally merged into the Saxon Electorate in 1423.

Supporting paragraphs: Posen-West Prussia Weimar Republic
Answer: Weimar Republic