Free software (free software)
"Free software" means software that respects users' freedom and community. Roughly, it means that the users have the freedom to run, copy, distribute, study, change and improve the software. Thus, "free software" is a matter of liberty, not price [1].
"Free software" gives users access to source code. Users have the rights to use the software, redistribute it, modify it, and distribute their modifications. Users can receive payment for these distributions. However, since any user can redistribute as many copies of the software as they would like, the price is normally very close to the cost of media. Other than the copylefted* conditions below there are virtually no restrictions on the use of the software or how it can be modified. This includes primarily public domain software and copylefted software[2].
Attention focused on free software is that the user absolute control over the software, free to run, copy, distribute, study, change and improve the software, not for the software is free or not . If a software is free software, it needs to provide the following four degrees of freedom [1] :
Freedom 0: The freedom to run the program as you wish, for any purpose. Whatever the purpose, the user is free to run the software.
Freedom 1: The freedom to study how the program works, and change it so it does your computing as you wish Access to the source code is a precondition for this.. Users are free to study and modify the software used to achieve desired by the user calculation. Provided that the users get software source code.
Freedom 2: The freedom to redistribute copies so you can help others. Users can freely distribute copy of the software used to help others.
Freedom 3: The freedom to distribute copies of your modified versions to others By doing this you can give the whole community a chance to benefit from your changes Access to the source code is a precodition for this... The user can freely distribute the software after the modified copy, so the whole community can benefit from the modified software. It is provided for obtaining the source code of the software.
Visibility, access to the software source code is a necessary condition for a free software. Users are free to modify the software and distribute it to others without any permission. Free software is usually more reliable than non-free software.
Open source software (open source software)
"Open source software" is used by some people to mean more or less the same category as free software. It is not exactly the same class of software: they accept some licenses that we consider too restrictive, and there are free software licenses they have not accepted. However, the differences in extension of the category are small: we know of only a few cases of source code that is open source but not free. In principle it could happen that some free programs are rejected as open source, but we don't know if that has ever happened[3].
Open-source software and free software is somewhat similar meaning and, therefore, are often confused. But it can be seen from the above, the open-source software is only part of the free software, and can not completely replace the free software. Developers prefer to use the term "free software" is.
Public software (public domain software)
"Public domain software" is source code that has no restrictions on use or distribution. It can be used in any way, copied, modified, distributed, and sold with any added licensing terms desired[2].
"Public domain software" is software that is not copyrighted. If the source code is in the public domain, that is a special case of non-copylefted free software, which means that some copies or modified versions may not be free at all[3].
Public software is not copyrighted , and therefore the modified software is added after the license is no longer some freedom. Therefore we can say the public is not copylefted software's.
Proprietary software (proprietary software)
“Proprietary software” is the traditional commercial model. Software executables are sold or leased with no user right to distribute the executable to others. Commercial licensing terms very, but limited copying rights may apply for backups or for other fair uses that do not deprive the software vendor from rightful income under its license. Source code is not provided under this model[2].
Proprietary software source code is not available, the user does not distribute, replicate, the right to modify.
Shareware (shareware)
Shareware executables have no restrictions on distribution, but users are required to pay for the software under the honor system if they decide to use it. Source code is not provided[2].
Shareware is software which comes with permission for people to redistribute copies, but says that anyone who continues to use a copy is required to pay a license fee[3].
Shareware software does not limit the spread, but does not provide the source code, you want to use the software required to pay fees. Therefore Shareware is not free software.
Copyleft software (copylefted software)
"Copylefted software" is free software that has been copyrighted so that the users rights modify and redistribute the source code are always transferred to subsequent users[2].
"Copylefted software" is free software whose distribution terms ensure that all copies of all versions carry more or less the same distribution terms[3].
Copyright-free software is a free software, software modified by the user at the time of spreading to comply with the terms of the original software and licensing. GNU release of General Public License (GPL) is a specific copyleft license to ensure that free software is free for all users.
Reference
[1].https://www.gnu.org/philosophy/free-sw.en.html
[2].Shackleford W P, Proctor F M. Use of open source distribution for a machine tool controller[C]//Sensors and Controls for Intelligent Manufacturing. International Society for Optics and Photonics, 2001, 4191: 19-30.
[3].https://www.gnu.org/philosophy/categories.en.html
* Copyleft copyleft, is a concept developed by the free software movement, is a use of the existing copyright system to protect the freedom of all users License and secondary developers. Increase copyleft free software license terms in the way, in addition to the free software allows the user to freely use, walking, modify the outside, copyleft license also requires the user to modify derivative works must be based on equal License released to contribute to the community. --Baidu Encyclopedia