This is the 13000th most frequent Polish word.
oddzielną
"Oddzielną" means "separate" in English.
The word "oddzielną" is used here as an adjective, agreeing with the feminine noun "salę" to describe it as being separate or distinct.
Potrzebuję oddzielną salę na spotkanie.
I need a separate room for the meeting.
In this context, "oddzielną" modifies the feminine noun "książkę," indicating individual possession or allocation.
Każde dziecko ma oddzielną książkę do nauki.
Each child has a separate book for studying.
Here, "oddzielną" is tailored to match the feminine noun "fakturę," signifying its individuality among potential others.