An OS (Operating System) is software that manages computer hardware and software resources. It provides a user interface, allowing users to interact with the computer and run applications. Common examples of operating systems include Windows, macOS, and Linux. The OS acts as a bridge between users and the computer's hardware, ensuring that different programs can run smoothly without interfering with each other. It handles tasks such as memory management, file storage, and device control, making it essential for the overall functionality of a computer or mobile device.