Acording to the FHS, the directories
/usr/lib are both for libraries (libraries used in
/sbin and user libraries, respectively).
But what about the
/var/lib folder? Following the same logic this folder should have something like "variable libraries" (that sounds strange) but it actually holds data generated and maintained by running programs, or as defined by the wikipedia article:
State information. Persistent data modified by programs as they run, e.g., databases, packaging system metadata, etc.
From a fresh view, it makes more sense to put database data and served files under
/srv instead of