This is the 71st most frequent Polish word.
kilka
"Kilka" means "a few" or "several" in English.
The Polish word 'kilka' is used here to convey a small number of objects, in this case, books, and serves as a quantifier.
Mam kilka książek.
I have a few books.
In this sentence, 'kilka' refers to an unspecified but small number of people in the context of attendance.
Kilka osób przyszło na spotkanie.
A few people came to the meeting.
Here, 'kilka' quantifies a small number of days to indicate the duration of the action described.