Sourcebook
A sourcebook is a collection of writings on a subject that is intended to be a basic introduction to the topic presented. Academic use. In American universities, a sourcebook, either a standard one or a custom collection, may function as a supplement or replacement for a textbook. In American law schools, casebooks are similar to sourcebooks, offering selections of legal cases and commentary, forming the basis for analysis and discussion. Games. In games, a "sourcebook" is a publication intended to supplement the core materials of a gaming product. Sourcebooks are most commonly used to complement role-playing games and  some tabletop or wargaming series, and often contain optional rules, scenarios, or other materials that players can use to extend or enhance the central game. The term tends to refer to an overall expansion, while the related splatbook focuses on a specific fictional aspect of the game in depth. Popular gaming series with many sourcebooks include: