Free and Open Source Software (or FOSS) is software that is licensed under one of several accepted free software1 or open source licenses2 that: do not restrict your ability to run the software, for any purpose, provide one with access to the source code, permit one to modify the software, permit one to share verbatim copies of the software with others, and * under certain conditions, allow one to share one's modifications with others.

See "What is Free Software?"3 and also "The Open Source Definition."4