3.9. Mount points and disk partitions
In Red Hat Enterprise Linux, each partition forms a part of the storage, necessary to support a single set of files and directories. Mounting a partition makes the storage of that partition available, starting at the specified directory known as a mount point.
For example, if partition /dev/sda5 is mounted on /usr/, it means that all files and directories under /usr/ physically reside on /dev/sda5. The file /usr/share/doc/FAQ/txt/Linux-FAQ resides on /dev/sda5, while the file /etc/gdm/custom.conf does not.
Continuing the example, it is also possible that one or more directories below /usr/ would be mount points for other partitions. For example, /usr/local/man/whatis resides on /dev/sda7, rather than on /dev/sda5, if /usr/local includes a mounted /dev/sda7 partition.