A card certifying the bearer's right to use the library(noun)
WordNet. Princeton University. 2010.
Use "library card" in a sentence
"Crunched between her Visa and her library card was a gold-embossed business card."
"Some great examples of this idea being put into practice are the success of farmers markets across the country, or the Tool Lending Library in the Berkeley Public Library system: anyone with a library card can borrow hammers, drills, ladders—for free!"