Luc Desfosses created the CISSP Work Notes, a page where Luc documented everything he encountered while studying for the CISSP.

It has a lot of good information for CISSP candidates. Like, How to study for the CISSP exam, fundamental CISSP concepts, and an index of IT and cybersecurity acronyms and abbreviations, as well as definitions.

Another good free resource if you need a quick reference or review before taking the exam.