This is the 415th most frequent Lithuanian word.
marijampolės
"Marijampolės" refers to something "of Marijampolė," a city in Lithuania.
In this sentence, 'Marijampolės' is in the genitive case, functioning as a possessive noun to denote the name of the city.
Marijampolės miestas yra gražus.
The city of Marijampolė is beautiful.
Here, 'Marijampolės' is used in the genitive case to modify 'muziejuje', showing ownership of the museum by the city.
Apsilankiau Marijampolės muziejuje.
I visited the museum of Marijampolė.
In this example, 'Marijampolės' accompanies 'bibliotekoje' to specify the library belonging to Marijampolė, demonstrating its possessive genitive usage.