A software license is a legal instrument governing the usage or redistribution of software. All software is copyright protected, irrespective of whether it is in the public domain. A typical software license grants an end-user permission to use one or more copies of software in ways where such a use would otherwise constitute copyright infringement of the software owner's exclusive rights under copyright law.
Software licenses can generally be fit into the following categories: proprietary licenses and free and open source licenses, which include free software licenses and other open source licenses.
The hallmark of proprietary software licenses is that the software publisher grants a license to use one or more copies of software, but that ownership of those copies remains with the software publisher. One consequence of this feature of proprietary software licenses is that virtually all rights regarding the software are reserved by the software publisher. Only a very limited set of well-defined rights are conceded to the end-user.
One example of such a proprietary software license is the license for Microsoft Windows. performance tests.
Free and open source software
With a free software license, in contrast to proprietary software licenses, ownership of a particular copy of the software does not remain with the software publisher. Instead, ownership of the copy is transferred to the end-user. As a result, the end-user is, by default, afforded all rights granted by copyright law to the copy owner.
A primary consequence of the free software form of licensing is that acceptance of the license is essentially optional—the end-user may use the software without accepting the license. However, if the end-user wishes to exercise any of the additional rights granted by a free software license (such as the right to redistribute the software), then the end-user must accept, and be bound by, the software license.
Open source licenses generally fall under two categories:
1>CopyLeft Licences: Those that aim to preserve the freedom and openness of the software itself come under the 'copyleft' licenses.
An example of a copyleft Free Software license is the GNU General Public License (GPL). This license is aimed at giving the end-user significant permission, such as permission to redistribute, reverse engineer, or otherwise modify the software. But,the end-user must comply with certain terms if the end-user wishes to exercise these extra permissions granted by the GPL. For instance, any modifications made and redistributed by the end-user must include the source code for these..
2>Permissive free software license: Those that aim to give freedom to the users of that software come under permissive licenses.
Examples of permissive free software licenses are the BSD license and the MIT license, which essentially grant the end-user permission to do anything they wish with the source code in question, including the right to take the code and use it as part of closed-source software or software released under a proprietary software license.