A "mount point" is a concept probably originating with unix filesystems, though other OSes may have a similar concept.
A unix filesystem consists of a hierarchy of directories. The first filesystem to be mounted (made accessible) is the root filesystem. It is mounted at "/", that is, "/" is the root filesystem's mount point. Other filesystems are mounted "on top of" directories that are part of the root filesystem.
For example, there is often a filesystem mounted on "/usr", (less often these days, but in the old days) and so "/usr" is the "mount point" for this filesystem.
Filesystems are "mounted" with the "mount" command, which typically looks something like this:
% mount -t ufs /dev/someblockdevice /some/mount/point
The "-t ufs" tells the OS what kind of filesystem, in this case ufs, other kinds would be NFS, MSDOS, vxfs, s5, ext2, cdfs to name a few.
The "-t" is one of the things unix vendors seem to loveto change for no good reason. I've seen "-f", "-F", and "-v" used in place of "-t".
the "/dev/someblockdevice" is the device node of typically, a disk device, and tells the OS which physical device is being accessed. Some (most) variants of unix distinguish between a character devices (aka raw devices) and block devices, the difference being that I/O performed through the character interface to a disk device does not go through the buffer cache while I/O operations performed on the block device do go through the buffer cache. Anyway, you typically use the block interface to a disk device for purposes of mounting it.
the "/some/mount/point" is the "mount point", where in the filesystem tree you would like the filesystem on this device to appear.
This write-up was a response to a node-shell challenge I happened to overhear in the chatterbox. Nobody else seemed to have a very clear idea what a "mount point" was, so I volunteered.
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