Lithuania proper

Lithuania proper refers to a region which existed within the Grand Duchy of Lithuania, and where the Lithuanian language was spoken. The primary meaning is identical to the Duchy of Lithuania, a land around which the Grand Duchy of Lithuania evolved. The territory can be traced by Catholic Christian parishes established in pagan Baltic lands of the Grand Duchy of Lithuania subsequent to the Christianization of Lithuania in 1387. The Lithuania Proper was always distinguished from the Ruthenian lands, the Lithuanians differed from the Ruthenians in their language and faith . The term in Latin was widely used during the Middle Ages and can be found in numerous historical maps until World War I.
Lithuania proper sometimes is also called Lithuania Major, particularly in contrast with Lithuania Minor.

Wikipedia