A computer operating system that allows multiple users to access it at the same time.
UNIX is a multi-tasking and stable operating system for desktops, servers and laptops. It contains a GUI (Graphical User Interface) that offers an easy usage. MacOS X, Linux/GUI and Sun Solaris are the most common varieties of UNIX. The UNIX operating system contains the shell, the kernel and the programs. The kernel is the hub of the UNIX operating system. Whereas, the shell is an interface between the kernel and the user.