FLOSS UK ... Free and Libre Open Source Software UK
We used to be called the UK Unix Users Group so you may still see some web resources and email addresses by that name too.
There are many computer operating systems either descended from or at least inspired by the original Unix system as designed by AT&T back in the 1970s.
The main thing that made Unix a success back in the early days was a willingness for people to co-operate and share the source code of software they were developing.
This notion is now called by any of the terms in the new group title. The new title makes explicit what was implicit in the choice to use Unix and allows the group to remain relevant as the underlying software rapidly evolves for the 21st century.
Floss stands for Free and Libre Open Source Software. The term Libre is used because the meaning of Free in English is ambiguous. It can mean both free as in gratis - 'a free lunch' and the freedom to take what is already known and given and be able to build upon it. This principle is itself hundreds if not thousands of years old and forms the basis of scholarship and the scientific method.
Standing on the shoulders of giants is the common phrase used to convey the benefit that humanity has gained from this co-operative way of working.
See also the Wikipedia article for further information on the Free vs. Libre distinction.
Free software has been an important part of the appeal of the Unix operating system ever since its first days. Academic institutions were granted source licenses to AT&T Unix and form the early days made and shared with each other important contributions such as the first TCP/IP networking that allowed the early Internet to exist that was developed in BSD Unix.
This is why it is natural now for the UK Unix Users Group to evolve into FLOSS UK. Most (but not all) free and Open Source software is available for Operating Systems in the Unix mind-set which consists of the many variants of Linux, Berkley Unix (BSD) based systems including Apple OS X and also for the remaining commercial Unixes such as AIX, Solaris, HP/UX etc.. Much of the software is also available for 'unlike Unix' proprietary Operating Systems, the only one of which still in common use being Microsoft Windows. This flexibility of Open Source makes it possible to try some individual Open Source programs without having to take the leap of leaving the 'other' world behind entirely.
Many millions of people have made such a jump however, leaving Windows use as occasional to none and now enjoy computer reliability measured in months of uptime and no need for the constant anti-virus war of nerves.
It is even possible thanks to some clever projects such as Wine to take some of your legacy software from the Windows world with you when you make the move to a free OS platform.