Free and open source software, also F/OSS, FOSS, or FLOSS (free/libre/open source software) is software which is liberally licensed to grant the right of users to study, change, and improve its design through the availability of its source code. This approach has gained both momentum and acceptance as the potential benefits have been increasingly recognized by both individuals and corporate players.

'F/OSS' is an inclusive term generally synonymous with both free software and open source software which describe similar development models, but with differing cultures and philosophies. 'Free software' focuses on the philosophical freedoms it gives to users and 'open source' focuses on the perceived strengths of its peer-to-peer development model. Many people relate to both aspects and so 'F/OSS' is a term that can be used without particular bias towards either camp.

Free software licenses and Open-source licenses are used by many software packages. The licenses have important differences, which mirror the differences in the ways the two kinds of software can be used and distributed and reflect differences in the philosophy behind the two.

Today the terms "free software" and "free open source software" (FOSS) and "free libre open source software" (FLOSS) generally mean the same thing. Despite disagreements about independently important but relatively minor differences, the simple term "open source" originally had the same meaning as FOSS/FLOSS for several years, nicely guarded, but not trademarked, by the Open Source Initiative. However, by mid 2007 enough companies were opening some source to hop on the open source bandwagon, while keeping other advanced functionality closed, that the common meaning of "open source" came to include what is now called "Commercial Open Source Software" (COSS) as well. Today either the specific terms free software/FOSS/FLOSS or COSS are often used instead of the more general term "open source" in order to differentiate between the two different models and preserve the original meaning of the free software/FOSS/FLOSS space.

Source: [1] Wikipedia - FOSS; http://tr.im/o4Jl