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.

The first OS installed in a computer. In a virtual machine environment, there may be a host operating system that interacts with the virtual machine monitor, which manages the virtual machines.

Today’s operating systems are more sophisticated and feature-rich than ever before, which makes them substantially more useful to the enterprise but also adds to security vulnerability—unless the ...