This is the 1624th most frequent Polish word.
najbliższym
"Najbliższym" means "the nearest" or "the closest" in English.
The word 'najbliższym' is used here as an adjective in the instrumental case, describing 'tygodniu' ('week') to mean 'next' or 'upcoming'.
W najbliższym tygodniu spotkamy się w Warszawie.
Next week, we will meet in Warsaw.
Here, 'najbliższym' functions as an adjective in the instrumental case describing 'sąsiadem' ('neighbor') to mean 'closest' or 'nearest'.
Najbliższym sąsiadem naszej szkoły jest biblioteka.
The closest neighbor to our school is the library.
In this sentence, 'najbliższym' is used as an adjective in the locative case, describing 'spotkaniu' ('meeting') to indicate the upcoming meeting in terms of time.