FLOSS is an abbreviation that stands for "Free/Libre Open Source Software". It refers to software that is not only free because you don't have to pay money for it. But it is also free to be used for any purpose you want.
There is a whole ecosystem of such software, that is centered mostly around the GNU and Linux communities, but reaches far beyond. The Open Movie Editor is part of that Community or Movement.
There is plenty of Information available about the FLOSS Movement, the following list of links is just a starting point for your research.