[Wrapper-user] run levels

[Ramachandra, A. <Ram...@Sy...>]

The help docs for starting the wrapperlistener app at reboot says:
"We will want our application to be started for all multi-user run levels
and stopped for the halt, single-user and reboot runlevels."

I did not quite understand what this means.
Could anybody please explain? What exactly is meant by a run level?

 -Thanks
 -Arun