Linux is a free and open-source operating system that was created as a free alternative to proprietary operating systems like UNIX. It was started in 1991 by Linus Torvalds and has grown significantly since then. The document provides an overview of Linux, including its history and origins from UNIX, the GNU project, and early versions developed by Linus Torvalds and others. It describes the growth of Linux and popular distributions like Red Hat, Debian, and Ubuntu. It also summarizes the key components of a default Linux desktop environment.