Non-Fiction vs Fiction
Non-Fiction Books: Non-fiction is writing based on fact and real events. Non-fiction writing can be objective or subjective, and it can be presented as a story, sometimes called "narrative non-fiction." When conducting research, students almost always use non-fiction books unless conducting literary research.
Fiction Books: Fiction is literature in the form of prose, especially novels, that describes imaginary characters and events. In general, fiction is read for its literary qualities or for casual, "pleasure" reading. At TAS fiction is read, analyzed, and researched extensively in English courses, but its use outside of literary studies--in history or political-science research, for instance--is quite limited. For that reason, when talking about books for research, the focus is on non-fiction books.
Print vs digital (eBooks)
Increasing numbers of eBooks are "born digital," but most eBooks for research--like those in our TAS databases and e-book collections--were originally print books, later digitized as eBooks. This means the content is exactly the same, so unless your assignment specifically requires a "print" format, your choice of print or digital book depends on where you can find the best information.