827
OS market share in Top 500 supercomputers
(feddit.org)
From Wikipedia, the free encyclopedia
Linux is a family of open source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991 by Linus Torvalds. Linux is typically packaged in a Linux distribution (or distro for short).
Distributions include the Linux kernel and supporting system software and libraries, many of which are provided by the GNU Project. Many Linux distributions use the word "Linux" in their name, but the Free Software Foundation uses the name GNU/Linux to emphasize the importance of GNU software, causing some controversy.
Community icon by Alpár-Etele Méder, licensed under CC BY 3.0
To make it more specific I guess, what's the problem with that? It's like having a "people living on boats" and "people with no long term address". You could include the former in the latter, but then you are just conveying less information.
Others have answered, but it is interesting to know the history of UNIX and why this came to be. BSD is technically UNIX derived, but being more specific isn't the reason why it has distinct branding. As with many evils the root is money, and there's a lot in play into how it all happened, including AT&T being a phone monopoly.
https://en.wikipedia.org/wiki/UNIX_System_Laboratories,_Inc._v._Berkeley_Software_Design,_Inc.
And I recommend watching this video informative and funny about the history and drama behind it all: https://www.youtube.com/watch?v=g7tvI6JCXD0