When you have finished using the system, you should log out. Leaving your terminal session unattended poses a security risk, as someone else could approach your terminal while you are away. Leaving an idle session logged in also consumes a small, but real, portion of system resources.
Log out using either the LOGOUT or the LOGOUT/FULL command:
$ LOGOUT MIKE logged out at 12-DEC-2002 19:07:39.58
or
$ LOGOUT/FULL MIKE logged out at 12-DEC-2002 19:08:52.31 Accounting information: Buffered I/O count: 127 Peak working set size: 1771 Direct I/O count: 50 Peak page file size: 5955 Page faults: 10417 Mounted volumes: 0 Charged CPU time: 0 00:00:04.80 Elapsed time: 0 00:00:48.02