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.

What began as a Finnish student's personal project in 1991 has transformed into a global computing powerhouse. Linus Torvalds ...

Just about every piece of technology has some form of an operating system – desktops, laptops, mobile phones, and servers, to name just a few. The Merriam-Webster definition of an operating system?

I've used nearly every possible desktop operating system known. I've experienced nearly every incarnation of Windows and MacOS, I've used just about all the various Linux distributions over the years, ...