a preset operating state on a Unix-like operating system

a shorthand way to tell the system to get into a certain state of configuration with respects to what services are running (daemons, see below), whether to allow remote logins, what filesystems are mounted read-only or read-write, etc

a software configuration of the system that allows only a selected group of processes to exist

a state for the system

a state, or mode , that is defined by the services listed in the directory /etc/rc

a state the system is running in

The overall system state as defined by init. Runlevel 6 is rebooting, runlevel 1 is "single user mode", runlevel 4 is an X login, etc. There are 6 available runlevels on a Slackware system.

Specifies which system services are started up when Linux boots. Different runlevels start the services necessary for networking, multiple users, and graphical login sessions. The default runlevel for a Red Hat Linux graphical workstation is 5.

The term runlevel refers to a mode of operation in one of the computer operating systems that implement Unix System V-style initialization. Conventionally, seven runlevels exist, numbered from zero to six.