These terms often refer to Google Dorking (Google Hacking), a method of using advanced operators to find information that is not easily accessible through a standard search. "GGLC" may be a shorthand for "Google Local" or a specific internal document tagging system.
In some contexts, these specific alphanumeric codes (like JP4VER) correspond to military or governmental joint publications that have been indexed by Google but aren't linked on main websites. How to Use This "Trick" Safely
This tells Google to only show results from Google Docs that contain the term "JP4VER" and are in PDF format. Search Google like a Pro!