document updated 10 years ago, on Apr 23, 2012

summaries of what the various directories are "intended" for
- [authoritative] Filesystem Hierarchy Standard
- [authoritative] hier(7) — this has existed since V7 in 1979
- [authoritative] Solaris's filesystem(5) or filesystem(7)
- [authoritative] XDG's Base Directory Specification (full specification) ("what is XDG?")
- wikipedia (more)
home-grown scripts are SUPPOSED to go in /usr/local/, instead of /usr/
- though some people dispute this
/tmp/ is supposed to be cleaned out every boot, while files in /var/tmp/ stick around until manually removed [1] [2]