自由软件（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].

自由软件关注的重点在于用户对软件的绝对支配权，可以自由地运行、复制、散布、学习、修改并改进该软件，而不在于软件是免费与否。如果一个软件为自由软件，那么它需要提供以下四种自由度^[1]：

Freedom 0: The freedom to run the program as you wish, for any purpose. 无论何种目的，用户可以自由地运行该软件。

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. 用户可以自由地学习并修改该软件用于实现用户想得到的计算。前提是用户得到软件的源代码。

Freedom 2: The freedom to redistribute copies so you can help others. 用户可以自由地散布该软件的复制用于帮助别人。

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. 用户可以自由地散布该软件修改后的复制，因此整个社区都可以得益于修改后的软件。前提是用于得到软件的源代码。

可见，访问软件源代码是其成为自由软件的必要条件。用户可以自由地修改软件并散布给其他人而不需要任何许可。通常自由软件都比非自由软件更加可靠。

开放源代码软件（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].

开放源代码软件与自由软件的含义有些类似，因此也经常被混淆。但是从上面可以看出，开放源代码软件只是自由软件的一部分，并不能完全替代自由软件。开发者更倾向于使用“自由软件”的概念。

 公共软件（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].

公共软件没有版权，因此修改后的软件被添加了一些许可后就不再是自由的了。因此可以说公共软件不是copylefted的。

私有软件（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].

私有软件不提供源代码，用户也没有散布、复制、修改的权利。

共享软件（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].

共享软件不限制软件的散布，但是不提供源代码，想要使用该软件需要支付费用。因此共享软件并不是自由软件。

版权所无软件（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].

版权所无软件是一种自由软件，用户修改后的软件在散布时要遵守原始软件的条款和许可。GNU发布的General Public License (GPL)是一个特定的版权所无许可，用以保证自由软件对所有用户是自由的。

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 著佐权，是一个由自由软件运动所发展的概念，是一种利用现有著作权体制来保护所有用户和二次开发者的自由的授权方式。在自由软件授权方式中增加著佐权条款后，该自由软件除了允许使用者自由使用、散步、修改之外，著佐权许可证更要求使用者修改后的衍生作品必须要以同等的授权方式释出以回馈社会。——百度百科