"Reference books" are books that provide information about different subjects. They are used to look up specific facts, definitions, or explanations, like dictionaries, encyclopedias, or atlases. Full definition
We have the back of well established libraries and a good number of reference books of all subjects. (essayscampus.com)
You may have listed this, and I didn't find it, but it might be nice to include a list of reference books on the different methods of training. (pottytrainingconcepts.com)
As well as reference books, there are also, of course, many very long novels. (rogerpacker.com)