An operating system (OS) is a system software that manages computer hardware resources and provides common services for computer programs. It acts as a mediator between the user, the computer hardware, and the applications running on it. The operating system is responsible for ensuring that the computer's hardware components, such as the processor, memory, input/output devices, and storage devices, are functioning correctly and efficiently.

The operating system provides a user interface that enables users to interact with the computer and its applications. It also manages the allocation of system resources, such as memory, CPU time, and disk space, to ensure that each application has the resources it needs to run smoothly. The operating system also provides security features to protect the system from unauthorized access and ensure data integrity.