What is a Reference Book?
Reference materials are sources that provide a broad overview on a topic. They are typically "scholarly" and written by experts in a field, HOWEVER they aren't always considered "peer reviewed" are should not usually be cited directly in a paper. They are excellent starting points and will direct you toward useful peer-reviewed materials. You typically won't want to use a reference work as a cited source in your works, however they are excellent if you need a quick overview on a topic, or if you need to quickly identify seminal works (which you can cite!) on your topic.
A Few Philosophy Reference Materials of Particular Note:
While you don't typically cite these are sources in papers, they are very good starting points and help you:
Example:
My initial search was for "mind upload" but the entry in Encyclopedia of artificial intelligence : the past, present, and future of AI (Frana & M. J. Klein, Eds.) suggest I should instead use the term "whole brain emulation"