A textbook was a book used to educate students on a particular discipline.
In 2266, Captain James T. Kirk responded sarcastically to Doctor Leonard McCoy's concerns about Lieutenant Dave Bailey's performance as navigator, saying he'd been reading his textbooks again. McCoy countered by saying he didn't need textbooks to see that he might've promoted him too quickly. (TOS: "The Corbomite Maneuver")
In 2268, when Kirk asked Bela Okmyx what other books the Horizon had left behind on Sigma Iotia II, he said they included some textbooks on how to make radio sets and the like. (TOS: "A Piece of the Action")
When Beverly Crusher examined Data after the android beamed back from the SS Tsiolkovsky, she told him if he was any more perfect, she'd write him up in a Starfleet Medical textbook. He responded that he was already listed in several bio-mechanical texts. (TNG: "The Naked Now")
According to Data, some time before 2364, the clever strategy Jean-Luc Picard employed at the Battle of Maxia had made it into Starfleet textbooks. (TNG: "The Battle")
While informative, textbooks were not always helpful. In 2365, Data used the analogy of poker to attempt to explain to Commander Bruce Maddox why he felt that merely retrieving information from his positronic brain would preserve the facts, but not the feeling. He said that while he had read every treatise and textbook on the subject, he found out that actually playing the game was different than reading about it. (TNG: "The Measure Of A Man")
In 2375, Luther Sloan described Vice admiral Fujisaki's murder by food poisoning at the hands of Koval as a textbook operation. (DS9: "Inter Arma Enim Silent Leges")
Textbook response[]
Data gleaned from textbooks was often used as a baseline for individuals or objects of a similar type. In 2267, examination of nine male Omicron Ceti III colonists of varying ages showed textbook responses to all medical tests. (TOS: "This Side of Paradise")
In 2268, Spock expressed his surprise at the tricorder readings of the Kelvans, noting that they were almost classic textbook responses of the sort Humans would show. (TOS: "By Any Other Name")