Open-Source License

An open-source license is a copyright license for computer software that makes the source code available under terms that allow for modification and redistribution without having to pay the original author. Such licenses may have additional restrictions such as a requirement to preserve the name of the authors and the copyright statement within the code. One popular (and sometimes considered normative) set of open source licenses are those approved by the Open Source Initiative (OSI) based on their Open Source Definition (OSD).

Comparisons

There are also shared source licenses which have some similarities with open source, but a number of critical differences make such licenses incompatible with the Open Source Definition.

Some software licenses define an open standard basis and may or may not be similar to open source, for example PGP.

The Free Software Foundation has related but distinct criteria for evaluating whether or not a license qualifies a program as free software. See Free software license and Open source license. Likewise, the Debian project has its own criteria, the Debian Free Software Guidelines, which in many ways was a precursor to the Open Source Definition.

OSI approved licenses

Software in the public domain (that is, with no copyright license at all), meets those criteria as long as all source code is made available, and is therefore recognized by the OSI and entitled to use their service mark.

Non-OSI source licenses

Licenses that are source-available but not OSI-Certified include:

• HESSLA
• PGP
• MAME (source available, but not free software because it forbids commercial use and redistribution)