The /usr directory is for files that are shareable across a whole site. The /usr directory usually has its own partition, and it should be mountable read only. The following directories should be subdirectories of /usr:
/usr |- X11R6 |- bin |- dict |- doc |- etc |- games |- include |- info |- lib |- local |- man |- sbin |- share +- src
The X11R6 directory is for the X Window System (XFree86 on Red Hat Linux), bin is for executables, doc is for random non-man-page documentation, etc is for site-wide configuration files, include is for C header files, info is for GNU info files, lib is for libraries, man is for man pages, sbin is for system administration binaries (those that do not belong in /sbin), and src is for source code.