This is the 16596th most frequent Russian word.
северном
"Северном" means "northern" in English.
Here, 'северном' is used as an adjective describing the location of a district, emphasizing its geographical direction as north.
Я живу в северном районе города.
I live in the northern district of the city.
In this sentence, 'северном' is applied as an adjective to 'полюсе' (pole), specifying the North Pole as the location under discussion.
На северном полюсе всегда холодно.
It's always cold at the North Pole.
The term 'северном' in this sentence functions as an adjective modifying 'регионе' (region), indicating that the region in which the holiday was spent is located in the northern part.