"Turabian" is short-hand for a style guide authored initially by Kate Turabian and published by the University of Chicago Press. It represents the writing standard of most colleges and seminaries in matters of theology or biblical studies. The published style guide covers just about any research eventuality and should be consulted for serious research. For most of us . . . most of the time, it is enough to consult a short version of it. Fortunately, the University of Chicago offers just such a handy, online version. Here is a link:
Students often make mistakes in underlining or italicizing the names of series rather than books, referring to the editor of a series as the author, forgetting volume numbers on journal articles, or mixing up long and short forms of a footnote citation. If you want your work to be clean and professional, Kate Turabian can help you do it.