An operating system (often called an OS) is the main software that runs a computer and makes it possible to use all your programs and files. Without an operating system, your computer would just be a collection of chips and circuits that couldn't do anything useful.

Think of an operating system as the manager of everything happening inside your computer. When you click to open a game, the operating system finds that program and launches it. When you save a document, the operating system stores it in the right place on your hard drive. When you type on your keyboard or move your mouse, the operating system translates those actions so your programs understand what you want.

The operating system also acts like a referee, making sure different programs can all run at the same time without crashing into each other. If you're listening to music while writing a report and checking your email, the operating system coordinates all three programs, giving each one a turn to use the computer's processor.

Common operating systems include Windows (made by Microsoft), macOS (made by Apple), and Linux (which is free and open source). Phones also have operating systems: iOS for iPhones and Android for most other smartphones. Each operating system looks and works a bit differently, but they all do the same basic job of making computers usable for humans.