A directory in a FileSystem that doesn't itself have any contents, but is used to Mount another FileSystem in its place.

For example, your root file system / must exist on one 'volume' (partition). If you have /usr on another hard disk, you create an empty directory called /usr on the first hard disk, and you Mount the file system on the second disk to that mount point. You can then access the files in the /usr.

If you're unfamiliar with the standard Linux file layout, see FileSystemHierarchy.

Mountpoints are generally defined in fstab(5) and handled by mount(8).

Common Exmamples

/cdrom and /floppy

Linked to your floppy and CDROM drive (in fstab(5)), and empty until you put a disk in and mount it.

/mnt

A special case, /mnt is a directory that is defined by the Filesystem Hierarchy Standard as the MountPoint for a temporarily mounted file system.

This system is completely extensible - your filesystem can grow from / as far as it needs to grow.

Compare DriveLetters (which can't grow past 24 'mount points').