Normally when you log out from a session on a Linux system, any processes of yours that are still running get terminated. When you have long-running jobs, you may wish to log out while leaving those jobs running, and come back later to see how they are doing.
Two useful commands for this are:
nohup - no hangup - lets a job persist after you log out
screen - lets you preserve a login session, disconnect from it while leaving it running, and reconnect to it later