An operating system is foundational system software that manages computer hardware and provides an abstraction layer upon which application programs can execute. It functions as an intermediary between the user, the application software, and the physical hardware, coordinating the efficient use of computing resources. Core functionalities include process management, which schedules and controls concurrent tasks; memory management, which allocates and deallocates space in volatile memory; and I/O management, which facilitates communication between the computer and peripheral devices. By providing a stable, standardized environment, the operating system enables the execution of multiple, diverse applications simultaneously while maintaining data integrity and system stability.