A textbook which introduces vocabularies that could appear on the day of the test (TOEFL) gives me a below sentence.
It sounds like the staff at the circulation desk knows you pretty well. These days I'm mainly using the reserve desk and the reference section. My biology professor puts a lot of articles on reserve, and then there're these big reference volumes -- like The Encyclopedia Of Biology -- in the reference room that he wants us to read. You can't check those out. So I usually take them to a quiet desk up in the stacks and read them there.
I "conquered" several parts which are easy to native speakers, but I finally gave up when I came across the bold part. (Googling didn't help). Could you please help me what up in the stacks mean, in (probably) this context?