The Open Source Definition

The Open Source Definition is not a software license. Instead it is a specification of what is permissible in a software license for that software to be considered open source. The Open Source Definition is based on the Debian free software guidelines or social contract, which provides a framework for evaluating other free software licenses.
The Open Source Definition includes several criteria, which can be paraphrased as follows (OSI, 1999):

1. Free Redistribution – Copies of the software can be made at no cost.
2. Source Code – The source code must be distributed with the original work, as well as all derived works.
3. Derived Works – Modifications are allowed, however it is not required that the derived work be subject to the same license terms as the original work.
4. Integrity of the Author’s Source Code – Modifications to the original work may be restricted only if the distribution of patches is allowed. Derived works may be required to carry a different name or version number from the original software.
5. No Discrimination Against Persons or Groups – Discrimination against any person or group of persons is not allowed.
6. No Discrimination Against Fields of Endeavor – Restrictions preventing use of the software by a certain business or area of research are not allowed.
7. Distribution of License – Any terms should apply automatically without written authorization.
8. License Must Not Be Specific to a Product – Rights attached to a program must not depend on that program being part of a specific software distribution.
9. License Must Not Contaminate Other Software – Restrictions on other software distributed with the licensed software are not allowed.

The GNU GPL, BSD, X Consortium, MPL, and Artistic licenses are all examples of licenses that conform to the Open Source Definition.
The evaluation of a proposed license elicits considerable debate in the free software community. With the growing popularity of open source, many companies are developing licenses intended to capitalize on this interest. Some of these licenses conform to the Open Source Definition, however others do not. For example, the Sun Community Source License approximates some open source concepts, but it does not conform to the Open Source Definition. The Apple Public Source License, or APSL (Apple, 1999b), as been alternately endorsed and rejected by members of the open-source community.