What's the best way to think of software?
As a layer cake. Think about computer hardware as being at the bottom of the layer cake. The next layer is the operating system, the collection of programs that control the hardware. Windows, Mac OS X, iOS, and Linux are operating systems. On top of that layer are applications—a range of which include end-user programs like those in Office, apps that run on smartphones, and the complex set of programs that manage a business's inventory, payroll, and accounting. At the top of the cake are users.