Open Source is a recent term developed by a group of Linux and Free software developers and advocates. It carries more pragmatic connotations than Free Software, though both terms and both movements are still flourishing today. Open source software is not necessarily copylefted.
The term can refer to software that is available under an OSI-approved license; it can also apply more broadly to any software that operates under the general principles of openness, source sharing, and meritocratic development.
The term can also apply to the popular movement of individuals, organizations and companies that seek to put such software into mainstream usage. In this usage, Open Source is generally regarded as the more pragmatic, business-conscious movement, while Free Software proponents take a long-term, more idealistic perspective. Both camps have their acknowledged place in the development of Free and Open-Source Software (or FOSS or FLOSS for free libre and open-source software).
A common copyleft license is the GNU GPL. Sometimes, confusion arises regarding which is more "free" -- Open source or copyleft. The distinction is: open source software provides more freedom for the user to do what they wish with the code, copylefting keeps the software itself free (as in libre) by forbidding the user from incorporating the software into proprietary programs.
The Open Source Initiative defines an open source software license as open source if it meets these requirements (http://www.opensource.org/docs/definition_plain.php):
- The license shall not restrict any party from selling or giving away the software as a component of an aggregate software distribution containing programs from several different sources. The license shall not require a royalty or other fee for such sale.
- The program must include source code, and must allow distribution in source code as well as compiled form. Where some form of a product is not distributed with source code, there must be a well-publicized means of obtaining the source code for no more than a reasonable reproduction cost preferably, downloading via the Internet without charge. The source code must be the preferred form in which a programmer would modify the program. Deliberately obfuscated source code is not allowed. Intermediate forms such as the output of a preprocessor or translator are not allowed.
- The license must allow modifications and derived works, and must allow them to be distributed under the same terms as the license of the original software.
- The license may restrict source-code from being distributed in modified form only if the license allows the distribution of "patch files" with the source code for the purpose of modifying the program at build time. The license must explicitly permit distribution of software built from modified source code. The license may require derived works to carry a different name or version number from the original software.
- The license must not discriminate against any person or group of persons.
- The license must not restrict anyone from making use of the program in a specific field of endeavor. For example, it may not restrict the program from being used in a business, or from being used for genetic research.
- The rights attached to the program must apply to all to whom the program is redistributed without the need for execution of an additional license by those parties.
- The rights attached to the program must not depend on the program's being part of a particular software distribution. If the program is extracted from that distribution and used or distributed within the terms of the program's license, all parties to whom the program is redistributed should have the same rights as those that are granted in conjunction with the original software distribution.
- The license must not place restrictions on other software that is distributed along with the licensed software. For example, the license must not insist that all other programs distributed on the same medium must be open-source software.
- No provision of the license may be predicated on any individual technology or style of interface.