The /usr is pronounced like user, remember that it stands for Unix System Resources. The /usr hierarchy should contain shareable, read only data. Some people choose to mount /usr as read only. This can be done from its own partition or from a read only NFS share (NFS is discussed later).
The /usr/bin directory contains a lot of commands.
The /usr/include directory contains general use include files for C.
The /usr/lib directory contains libraries that are not directly executed by users or scripts.
The /usr/local directory can be used by an administrator to install software locally.
The /usr/share directory contains architecture independent data. As you can see, this is a fairly large directory.
The /usr/src directory is the recommended location for kernel source files.