An operating system is a collection of software that manages computer hardware resources and provides common services for programs. It allows multiple users and programs to run concurrently, allocating resources and providing file management, security, and other core functions. Key components of an operating system include the kernel, which handles processes, memory, devices and security; the user interface; and system utilities that support functions like booting and file management. Popular operating systems include Linux, an open-source version of UNIX with components like the kernel, system utilities and libraries.