A medical book or medical text was a reference book whose subject was medicine.
In 2153, Trip Tucker recognized characters on a sample box as Denobulan, having seen similar writing in Phlox's medical books. (ENT: "The Breach")
In 2155, John Frederick Paxton worried that it would only be a matter of time before rampant cross-breeding between Humans and aliens rendered the term "Human" worthy only of a footnote in a medical text. (ENT: "Terra Prime")
In 2267, James T. Kirk commented on Doctor Leonard McCoy's usage of a right hook to "convince" Eleen to let him examine her, saying he'd never seen that procedure in a medical book. McCoy replied, "It's in mine from now on." (TOS: "Friday's Child")
As of 2371, The Doctor's holoprogram contained the complete Bajoran medical text on Orkett's disease. He was thereby able to determine that a Cardassian bone marrow transplant could not be responsible for Cardassian genetic markers in Seska's blood, and therefore Seska was Cardassian, not Bajoran. (VOY: "State of Flux")
By 2372, Joseph Sisko had had so many of his original organs replaced by synthetic ones that he expected all of them to be replaced in a year or two, something he felt would earn him a write-up in the medical books. (DS9: "Homefront")
In 2374, The Doctor criticized Tom Paris for playing on the holodeck when he was behind in his studies of medical texts. (VOY: "Vis à Vis")
In 2401, former Starfleet doctor Beverly Crusher kept a copy of the Star Fleet Medical Reference Manual aboard her civilian vessel SS Eleos XII. (PIC: "Disengage")