The ethnic term "Prussian Lithuanians", "Lietuvininks" or "Lietuvininkai" generally refers to a Western Lithuanian ethnic group, who are of mixed Lithuania/German heritage.
The Lietuvininkai did not form a nation and were partially assimilated in to the Prussian Empire. They inhabited a small territory in East Prussia that was known as Prussian Lithuania or Lithuania Minor (Lithuanian: Prūsų Lietuva, Mažoji Lietuva, German: Preußisch-Litauen, Kleinlitauen). This ran in political contrast to the Grand Duchy of Lithuania, the Republic of Central Lithuania and later the Republic of Lithuania which all formed out of the Russian lands of Lithuania and, finally, the Prussian come League of Nations held Memel Territory.
The Lietuvininkai became Evangelical-Lutheran-Protestants after the Protestant Reformation. Most Lithuanians chose to remain Roman Catholic. Most of them forcibly were expelled by the Soviets after World War 2, with the remainder being sporadically expelled from the former Memel Territory in the 1950's.