Open Source Software is any program made publicly available for use and modification. It can be adapted for alternative needs, or bugs can be quickly found and fixed by the open community.
Free Software is open source software with a license requiring that any copy or derivative of the original code remain free and unrestricted in use.
Copylefted software: the program is copyrighted and released under a license that allows anyone to use, modify and distributed the work, but only if the same license is applied to the new work
Non-copylefted or permissive: an open source license that allows anyone to use, modify and distribute the work, but permits a proprietary license applied to the new work