Automounting is the process where mounting (and unmounting) of certain filesystems is done automatically by a daemon. If the filesystem is unmounted, and a user attempts to access it, it will be automatically (re)mounted. This is especially useful in large networked environments and for crossmounting filesystems between a few machines (especially ones which are not always online). It may also be very useful for removable devices, or a few other uses, such as easy switching between a forced-on ascii conversion mount of a dos filesystem and a forced-off ascii conversion mount of the same dos fs.
There are two types of automounters in linux; AMD and autofs. AMD is the automount daemon, and supposedly works like the SunOS AMD. It is implemented in user space, meaning it's not part of the kernel. It's not necessary for the kernel to understand automounting if you NFS mount to the local host, through the AMD daemon, which routes all automount filesystem traffic through the NFS system. Autofs is a newer system assisted by the kernel, meaning that the kernel's filesystem code knows where the automount mount points are on an otherwise normal underlying fs, and the automount program takes it from there. Only autofs will be described in this mini-howto.