umount

Unmount filesystems. Remove a special device or the remote node (rhost:path) from the filesystem tree at the point node. If either special or node are not provided, the appropriate information is taken from the fstab(5) file.

Syntax
      umount [-fv] special | node

      umount -a | -A [-fv] [-h host] [-t type]

Options
     -a      All the filesystems described in fstab(5) are unmounted.

     -A      All the currently mounted filesystems except the root are
             unmounted.

     -f      The filesystem is forcibly unmounted.  Active special devices
             continue to work, but all other files return errors if further
             accesses are attempted.  The root filesystem cannot be forcibly
             unmounted.

     -h host
             Only filesystems mounted from the specified host will be
             unmounted.  This option is implies the -A option and, unless
             otherwise specified with the -t option, will only unmount NFS
             filesystems.

     -t type
             Is used to indicate the actions should only be taken on filesystems
             of the specified type.  More than one type may be specified
             in a comma separated list.  The list of filesystem types can be
             prefixed with 'no' to specify the filesystem types for which
             action should not be taken.  For example, the umount command:

                umount -a -t nfs,hfs

             umounts all filesystems of the type NFS and HFS.

     -v
             Verbose, additional information is printed out as each filesystem
             is unmounted.

FILES
     /etc/fstab  filesystem table

“Be nice to people on the way up, because you’ll meet them on your way down” ~ Wilson Mizner

Related macOS commands

hdiutil - manipulate disk images.
mount - Mount a file system.
fstab(5) -