[Filesystem] /usr filesystem hierarchy

/usr/ hierarchy

/usr	- This directory is usually mounted from a separate partition. - It should hold only shareable, read-only data, so that it can be mounted by various machines running Linux.
/usr/lib	- Object libraries, including dynamic libraries, plus some executables which usually are not invoked directly. - More complicated programs may have whole subdirectories there.
/usr/lib/x86_64-linux-gnu	- Files associated with locally installed programs for 64-bit architecture
/usr/local/lib	- Files associated with locally installed programs.

resource
: https://superuser.com/questions/1352571/what-is-the-difference-between-usr-lib-usr-local-lib-and-usr-lib-x86-64-linux

: http://man7.org/linux/man-pages/man7/hier.7.html