Open source license

Publishers of open source software ordinarily do more than simply provide copies of both the source code and the object code when they distribute computer programs to the public. In addition, they establish the terms of use of the software by means of a license. A license is a contract through which the publisher allows recipients to use and modify the software, subject to certain conditions specified in the license. For example, the license might require that anyone who redistributes the software also make the source code of that software publicly available. A contract that provides users with a sufficient set of privileges to access and modify the software's source code is deemed an open source license.

The practice of preserving the rights of software users through a set of license provisions is sometimes called "copylefting." This term is a play on words on the term "copyright." Under this system, the copyright holder licenses the recipient of a copy of the software. The license permits the redistribution of further copies of the software &mdash; including software containing modifications &mdash; under the condition that those copies are subject to the same license. This legal framework ensures that derivatives of the licensed work remain open. If the licensee fails to distribute derivative works under the same license, then he may face legal consequences. In particular, the licensor could terminate the license, leaving the licensee without permission to copy, distribute, or modify the software.

Although no official definition specifies which software licenses qualify as open source licenses, an organization called the "Open Source Initiative," or OSI, has promulgated a widely followed set of standards. OSI describes itself as a "non-profit corporation dedicated to managing and promoting the Open Source Definition" through a certification program that it administers. To satisfy the Open Source Definition, the license must satisfy certain conditions, including:
 * 1) The publisher must provide both object and source code.
 * 2) The publisher must allow modification and redistribution of the code (with or without modifications by the licensee).
 * 3) The publisher must not limit distribution to certain fields of endeavor or products, or limit its use with other free software.

A number of different groups have promulgated a variety of open source licenses that OSI has certified as compliant with the "Open Source Definition." Among these is the General Public License or GPL.