This is the 7501st most frequent Polish word.
krajów
The word "krajów" in Polish means "of countries" or "of nations" (genitive plural form).
The word "krajów" here is the plural genitive form of "kraj" (country), used after the quantifier "kilka" (several).
Odwiedziłem kilka różnych krajów w Europie.
I visited several different countries in Europe.
The word "krajów" is used here in the plural genitive form to denote origin as required by the prepositional phrase "z różnych" (from various).
Dzieła sztuki z różnych krajów są wystawione na tej ekspozycji.
Artworks from various countries are exhibited in this display.
The word "krajów" is used as the plural genitive form to specify possession or association with "ekonomii" (economies).