Screen is an awesome utility that offers the ability to detach a long running process (or program, shell-script, irc window, etc.) from a session and then attach it back at a later time. Below are the basics:
To get started, enter:
screen
To see your existing screen sessions, enter:
screen -list
To detach an attached screen, enter:
screen -D
To re-attach to a detached screen, enter:
screen -r