Expansion books for
RPGs. Usually priced between 15 and 20
dollars, with some exceptions for some of the
mass-produced books companies like
White Wolf favor (so-called
splatbooks, or small books of 32 or 64 pages that
White Wolf also likes publishing for its
Aberrant superhero rpg.
First of the two types of sourcebooks are the expansions to the core rules, such as more toys to play with (whether magic or technological) or more types of characters to play.
Second are the types of books that further describe the setting of the game. These books typically advance the metaplot of the game's setting in some way, provide detailed information on a particular region of the setting, and/or provide detailed information of a particular group or organization within the setting.