A system software component that is external to the operating system kernel. If the phrase is used to refer to the operating system itself, it is redundant because an operating system "is" software.

An operating system that is designed for a server. Normally, it is a complete operating system with file, task and job management; however, with some earlier products, it was a separate component that ...

Hands up who believes that OS X and iOS are the most vulnerable operating systems in use today? Well, I find it a bit hard to believe, too, even though I’ve had a lot of hate-mail over the years for ...