Runlevel 0 (Halt): A system that has no daemons active in memory and is ready to be powered off.

Runlevel 1 (Single User Mode): A system that has only enough daemons to allow one user to log in and perform system maintenance tasks. A user is automatically logged in to the system as the root user when entering Single User Mode.

Runlevel 2 (Multiuser Mode) A system that has most daemons started and allows multiple users the ability to log in and use system services. Most common network services other than specialized network services are available in this runlevel as well.

Runlevel 3 (Extended Multiuser Mode): A system that has the same abilities as Multiuser Mode, yet with all extra networking services started (for example, SNMP, NFS).

Runlevel 4 (Custom):Not normally used, but can be customized to suit your needs.

Runlevel 5 (Graphical Mode): A system that has the same abilities as Extended Multiuser Mode, yet with a graphical login program called the GNOME Display Manager (gdm) started on tty7 that allows for graphical logins.

Runlevel 6 (Reboot): A special runlevel used to reboot the system.

Did this help or was it useful?? Are there errors??
Please post feed back so I can change them or know that I have helped.