Open Source as:
The Philosophy: A method and philosophy for software licensing and distribution designed to encourage use and improvement of software written by volunteers by ensuring that anyone can copy the source code and modify it freely.
In Modern Context: The term "open source" is now more widely used than the earlier term "free software" (promoted by the Free Software Foundation) but has broadly the same meaning - free of distribution restrictions, not necessarily free of charge.
The License: An open-source license is a type of license for computer software and other products that allows the source code, blueprint or design to be used, modified and/or shared under defined terms and conditions. This allows end users to review and modify the source code, blueprint or design for their own customization, curiosity or troubleshooting needs. Open-source licensed software is mostly available free of charge, though this does not necessarily have to be the case.
There are various open source licenses available. Programmers can choose an appropriate license to use when distributing their programs.