Software license

A software license is a legal instrument (usually by way of contract law, with or without printed material) governing the use or redistribution of software. Under United States copyright law all software is copyright protected, in source code as also object code form. The only exception is software in the public domain. A typical software license grants the licensee, typically an end-user, permission to use one or more copies of software in ways where such a use would otherwise potentially constitute copyright infringement of the software owner's exclusive rights under copyright law.

Software licenses and copyright law

Most distributed software can be categorized according their license types (see table).

Two common categories for software under copyright law, and therefore with licenses which grant the licensee specific rights, are proprietary software and free and open source software (FOSS). The distinct conceptual difference between both is the granting of rights to modify and re-use a software product obtained by a customer: FOSS software licenses the customer both rights and bundle therefore the modifiable source code with the software ("open-source"), proprietary software doesn't licenses typically these rights and keep the source code therefore hidden ("closed source").

Comparison of free and open-source software licenses

This is a comparison of published free software licenses and open-source licenses. The comparison only covers software licenses with a linked article for details, approved by at least one expert group at the FSF, the OSI, the Debian project, or the Fedora project. For a list of licenses not specifically intended for software, see List of free content licenses.

FOSS licenses

While the terms "free software license" and "open-source license" are both in wide use and usually interchangeable, "FOSS license" as both kinds unifying term exists. There is no one universally agreed-upon definition of FOSS software and various groups maintain approved lists of licenses. The Open Source Initiative is one such organization keeping a list of "open source" licenses. The Free Software Foundation maintains a list of what it considers free. The FSF's Free Software definition focuses on the user's unrestricted rights to use a program, to study and modify it, to copy it, and redistribute it for any purpose, which are considered by the FSF the four essential freedoms. The OSI's open-source criteria focuses on the availability of the source code and the advantages of an unrestricted and community driven development model.