From the LinuxFoundation.org:
"Linux is the world’s largest and most pervasive open source software project in the history of computing. The Linux kernel is the largest component of the Linux operating system and is charged with managing the hardware, running user programs, and maintaining the security and integrity of the whole system. It is this kernel which, after its initial release by Linus Torvalds in 1991, jump-started the development of Linux as a whole.
Linux has since become the world’s most dominant operating system, with massive adoption in almost every sector, including finance, government, education, and even film production. It is also the operating system of choice to support cutting-edge technologies such as the Internet of Things, cloud computing, and big data. It is helping to transform industries and disrupt the status quo."
You can install and run Linux on some platforms as part of the reference software stacks shipped with the Arm Reference Platforms deliverables.
Alternatively, visit the official GitHub repository or Linaro.