As opposed to software which is protected by strict licensing terms, Open Source Software (OSS) is computer software that is made available in source code form to the general public with much less stringent or indeed, non-existent copyright restrictions which are legally available to the copyright holder. Open source (OS) license terms tend to permit users to study, change, improve and distribute software more freely and are often used for software to be developed in a public, collaborative manner.
The actual definition “Open Source” was based on the Debian Free Software Guidelines, written and adapted in the US primarily by Bruce Perens in 1998/1999 and now used by the Open Source Initiative (OSI)1 to determine whether or not a software license can be considered “open source”. It means more than just access to the source code it also provides terms for distribution. OS licenses must comply with the following criteria:
“1. Free Redistribution
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.
2. Source Code
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.
3. Derived Works
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.
4. Integrity of the Author’s Source Code
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.
5. No Discrimination against Persons or Groups
The license must not discriminate against any person or group of persons.
6. No Discrimination against Fields of Endeavor.
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.
7. Distribution of License
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.
8. License Must Not Be Specific to a Product
The rights attached to the program must not depend on the program 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.
9. License Must Not Restrict Other Software
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.
10. License Must Be Technology-Neutral
No provision of the license may be predicated on any individual technology or style of interface.”
Open Source Initiative2
Software developers must decide if they want to publish their software with an OS license since any user will be able to develop the same software or understand its internal functioning. OSS also generally allows anyone to create modifications of the software, port it to new operating systems and processor architectures, share it with others or market it.
Although, OS licensing and distribution makes the source code publicly accessible, the authors may still fine tune such access by specific terms in the OS license.
The most prominent and widely used example of OS license is the GNU General Public License (GNU GPL or simply GPL), originally written by Richard Stallman for the GNU project.3 The GPL is reproduced in this Contract 18.
A similar OS license called ShareAlike is provided by Creative Commons, a non-profit organization founded by Lawrence Lessig. (See Contract 19.)
The GPL is the first “copyleft” license for general use, which means that derived works can only be distributed under the same license terms. Copyleft is a form of licensing which can be used to maintain copyright conditions for not only computer software but also for documents, music and art. In general, copyright law (as stated in detail above and extensively elsewhere in the Commentaries of this publication) is used by an author to prohibit others from reproducing, adapting, or distributing copies of the author’s work. In contrast, an author may give every person who receives a copy of a work permission to reproduce, adapt or distribute it and require that any resulting copies or adaptations are also bound by the same licensing agreement.
Copyleft licenses require that information necessary for reproducing and modifying the software must be made available to recipients of the executable.4 The source code files will usually contain a copy of the license terms and acknowledge the author(s).
The GPL grants the recipients of a computer program the rights of the free software definition and uses copyleft to ensure the freedoms are preserved, even when the work is changed or added to. This is in distinction to permissive free software licenses, of which the Berkeley Software Distribution (BSD) licenses5 are the standard examples.
The text of the GPL is not itself under the GPL. The license’s copyright disallows modification of the license. Copying and distributing the license is allowed since the GPL requires that recipients get “a copy of this License along with the Program”. According to the GPL FAQ, anyone can make a new license using a modified version of the GPL as long as he/she uses a different name for the license, doesn’t mention “GNU”, and removes the preamble, though the preamble can be used in a modified license if permission to use it is obtained from the Free Software Foundation (FSF).6
There has been a proliferation of OS licenses7> over the last 10 years which is one of the few negative aspects of the OS movement because it is often difficult to understand the legal implications of the differences between licenses. With more than 180,000 OS projects available and its more than 1,400 unique licenses, the complexity of deciding how to manage OS usage within “closed-source” commercial enterprises have dramatically increased. Some are home-grown while others are modeled after mainstream free and open source software (FOSS) licenses such as BSD, Apache, MIT-style (Massachusetts Institute of Technology), or GNU General Public License (GPL). In view of this, OS practitioners are starting to use classification schemes in which FOSS licenses are grouped (typically based on the existence and obligations imposed by the copyleft provision; and the strength of the copyleft provision).
Legally Binding: An important legal milestone for the FOSS movement was passed in 2008, when the US federal appeals court ruled that free software licenses definitely do set legally binding conditions on the use of copyrighted work, and they are therefore enforceable under existing copyright law.8 As a result, if end-users do violate the licensing conditions, their license disappears, meaning they are infringing copyright.
 The Open Source Initiative (OSI) was formed in February 1998 by Eric S. Raymond and Bruce Perens. With at least 20 years of evidence from case histories of closed software development versus open development already provided by the internet developer community, the OSI presented the “open source” case to commercial businesses, like Netscape. The OSI hoped that the usage of the label “open source,” would eliminate ambiguity, particularly for individuals who perceive “free software” as anti-commercial. They sought to bring a higher profile to the practical benefits of freely available source code, and they wanted to bring major software businesses and other high-tech industries into OS.  http://opensource.org/docs/osd.  The GNU Project is a free software, mass collaboration project, announced on September 27, 1983, by Richard Stallman at MIT. It initiated GNU operating system development in January, 1984. The founding goal of the project was, in the words of its initial announcement, to develop “a sufficient body of free software […] to get along without any software that is not free”. To make this happen, the GNU Project began working on an operating system called GNU (“GNU” is a recursive acronym that stands for “GNU’s Not Unix”). This goal of making a free software operating system was achieved in 1992 when the last gap in the GNU system, a kernel, was filled by the third-party Linux kernel being released as free software, under version 2 of the GNU GPL.  In computing, an executable file causes a computer “to perform indicated tasks according to encoded instructions” as opposed to a data file that must be parsed by a program to be meaningful. These instructions are traditionally machine code instructions for a physical CPU.  BSD, a Unix-like operating system, and the original owners of which were the Regents of the University of California where BSD was first written at the University of California, Berkeley.  The Free Software Foundation is the principal organizational sponsor of the GNU Operating System, whose mission is to preserve, protect and promote the freedom to use, study, copy, modify, and redistribute computer software, and to defend the rights of Free Software users.  Examples of FOSS licenses include Apache License, BSD license, GNU GPL, GNU Lesser General Public License, MIT License, Eclipse Public License and Mozilla Public License.  Jacobsen v Katzer 535 F.3d 1373 (Fed. Cir. 2008) and Software Freedom Conservancy, Inc v Best Buy Co, Inc, 2010 U.S. Dist. LEXIS 75208 (S.D.N.Y. July 27, 2010). See also Open Source Section B.VII in US Commentary.