Encyclopedia Gallifreya

The  was a sentient series of encyclopaedic volumes, (PROSE: Citation Needed) in the form of purple liquid in bottles, (TV: Journey to the Centre of the TARDIS) with one volume for each current incarnation of the Doctor. (PROSE: Citation Needed) Instead of being traditionally read, voices could be heard from within the bottles. The Eleventh Doctor kept this collection in his TARDIS library. (TV: Journey to the Centre of the TARDIS)

When Clara Oswald hid in the library to escape the time zombie that was following her, volume four of its 11 bottles began to spill. The vapour contained in the volume floated around the room, and voices speaking were heard. (TV: Journey to the Centre of the TARDIS)

Behind the scenes

 * The name was likely a Gallifreyan play on the Encyclopaedia Britannica.
 * On the BBC's official Doctor Who site, the work takes the older British spelling of Encyclopaedia Gallifreya.