= Free/Libre and Open Source Software also FOSS
An acronym covering both free software and open source software. The ethical foundations of the free software definition distinguish it from the open source definition which is grounded in the efficiency of the associated software development methodology and acceptability of the term "open source" in the software industry.
The inclusion of 'Libre' signals that the word free is used as in 'freedom' and not as in gratis.
It's similar to FOSS, Free Open Source Software, as well.