Linux is a fully-networked, multi-user, multitasking operating system similar to Unix. It was created in 1991 by Linus Torvalds and is now used widely due to its low cost, stability, and ability to run on different hardware platforms. Linux uses a command line interface where users log in and issue commands to perform tasks like copying files, installing software, and checking system resources. Common commands include ls to list files, cd to change directories, and man to view manuals.