This is the 853rd most frequent Hebrew word.
שניים
"Two" (masculine form in Hebrew).
The word 'שניים' is used here as a numeral indicating quantity, 'two' specifically for a pair of objects.
יש לי שניים של ספרים.
I have two books.
In this sentence, 'שניים' is used to describe a quantity associated with time, specifically two weeks.
הם באים לתקופה של שניים שבועות.
They are coming for a period of two weeks.
Here, 'שניים' acts as a quantity indicator suggesting a choice of two items among options.