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 is a master control program that runs the computer system. In all environments, except for specialized scientific and process control applications, the operating system (OS) ...

What is a guest OS (guest operating system)? A guest operating system is the operating system installed on either a virtual machine (VM) or partitioned disk. It is usually different from the host ...