An indirect mount is essentially a directory with automounts underneath it.
so... if /etc/auto.master has:
That's an indirect mount where auto.misc hold the info about the mounts to go under /misc. For
example, auto.misc might have:
Which means that access /misc/fred on the system running the automount will mount the NFS /export area off of fred and mount it to /misc/fred
A direct mount means something like the following it /etc/auto.master:
Which means /misc mounts export via NFS... no indirect directory above the automount point.
Support for direct mounts is relatively new (relatively being relative). So if you have a mix of new and old linux, you may be forced to just use indirect maps.