In computer security, a login or logon (also called logging in or on and signing in or on) is the process by which individual access to a computer system is controlled by identification of the user using credentials provided by the user.
A user can log in to a system to obtain access and can then log out or log off (perform a logout / logoff) when the access is no longer needed. To log out is to close off one's access to a computer system after having previously logged in.