An Operating System (OS) is software that manages computer hardware and software resources, providing a user interface and enabling applications to run. It acts as an intermediary between users and the computer hardware, controlling processes like memory management, file storage, input/output operations, and device management. Popular operating systems include Windows, macOS, and Linux. The OS ensures the efficient execution of programs, manages resources like CPU time and memory, and provides essential services such as security and error handling. It also allows users to interact with the system via graphical or command-line interfaces.