When you are talking about softwares, one does not consider an Operating System (OS) as a software, even though it is THE most important software on your device. I don’t blame anyone for this, as an OS is usually considered distinctively separate from the rest of the stuff which run on it. These bunch of stuff running on the OS are usually called as Softwares.
Anywhoo, coming back to topic at hand, Operating Systems. The major work of an OS is to provide an interface to user and system programs and translate the programs into hardware language. Ultimately, hardware is where the code executes, but for safety, security and convenience, every hardware interact with outer world through an OS in middle. And I am sure you will get more technical and specific explanation of what an OS is on the internet, so please feel free if there is a need.
Major OSes of the world are Windows, Mac OS, (various forms of) Linux, and some more Unix flavours.
Now, if you are using an Apple desktop or laptop, oh!! sorry, I mean a iMac or Macbook ( :P ), almost 100% chances are you are using a version of MacOS. And, if you are a normal user of