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.

program verification for operating system kernels, and computational linguistics Sean Grimes: Swarm intelligence, biologically inspired AI, multi-agent systems, software system design Gregory W.

it’s easy to forget that infrastructure software—everything from operating systems to middleware to databases—remains the foundation of every IT department and is critical for the operation ...

Contrast with application program. The following diagram shows the flow between system software and application software residing in memory in a multiuser computer. The operating system (OS), TP ...