Atlases – Show the Biblical world in maps. Maps may cover various places and time periods, address specific topics such as Paul’s journeys or the Exodus, and may contain supplementary drawings or photos.
Commentaries - Explain the scriptures verse by verse by providing detailed background information on the authorship, history, setting, and theme of the Gospel.
Concordances – List every word in the Bible and then direct the reader to every use of that work
Dictionaries – Provide definitions of words and expressions used in the Bible. Also identify proper names. Some dictionaries will also provide the original Greek or Hebrew.
Encyclopedias - Provide definitions and lengthy discussions beyond that found in dictionaries.
Gazetteers – Geographical dictionaries, sometimes with supporting pictures.
Handbooks/Guidebooks - Provide information or instruction on such topics as plants and animals of the Bible, dietary habits, weights and measures, calendars and holidays, etc.
Handbooks can also be on a specific topic such as Christian philosophy, prophesy, denominations,etc.
The best place to find an eBook is in OneSearch.
Search for your topic, and then limit your results to eBooks.
Reference databases are good for short, quick answers and for getting a general overview of a topic when starting your research.