does "Keep me signed in on this computer unless I log off"
you sign in, if you close your browser or after a period of inactivity,
your password will expire. But for your convenience, you can choose
to save your User ID and password on this computer. Your password
will be saved even if you disconnect from the Internet, close your
browser or turn off your computer. Your password will be saved until
you explicitly log off. As a safety measure, if you are using a
public computer or shared computer, you should always log off when
you are done using this system.