Have you ever started a long-running process in bash and wished you had ran it inside screen instead because you need to close your terminal session?
If you haven't heard of, or used disown before, it's a built-in command in the Bourne Again Shell that allows you to put that process in the background via bg and leave it running after you exit your shell. For example, doing
$ ./long-running-process $ bg $ disown $ exit
will leave your long-running-process running even after you exit. :)