A core rule book is typically the first book in a Role-Playing Game system that is released.
Within its pages, a reader would find the basic rules, often later expanded in expansion books
or splatbooks, some basic setting information, character creation rules and sometimes brief
narratives to set the style and feel of play one might expect.
Sometime the core rule book is broken up into two or three books, normally split between a book
for players, a book for the DM/GM/Referee of the game and if there is a third book, that is
normally a book of adversaries for the PCs to have conflicts with.
An example of this would be 2nd Edition Advanced Dungeons & Dragons game, which was originally
composed of the AD&D 2e Player's Handbook, the AD&D 2e Dungeon Master's Guide and the AD&D 2e Monster Manual.
