 <p>A better way to describe "mount" is "attach".</p> <p>The filesystem being mounted is attached to an empty directory of the existing filesystem. That is, the top level directory of the mounted filesystem becomes the directory on the existing filesystem.</p> <p>Subdirectories of the mounted filesystem become the subdirectories of the former directory on the existing filesystem, and so on.</p> <p>(The directory that was mounted on doesn't really have to be empty, but after mounting any contents it had are inaccessible, until the filesystem is unmounted).</p>