Free Software refers to the users' freedom to run, copy, distribute, study, change and improve the software. More precisely, it refers to four freedoms of software users:

The freedom to run the program, for any purpose (freedom 0).
The freedom to study how the program works, and adapt to your needs (freedom 1). Access to the source code is a precondition for this.
The freedom to redistribute copies so you can help your neighbor (freedom 2).
The freedom to improve the program, and release the improvements to others, so that the whole community benefits. (Freedom 3). Access to the source code is a precondition for this.
A program is free software if users have all these freedoms. Thus, you should have the freedom to redistribute copies, either with or without modifications, either gratis or charging a fee for distribution, to anyone anywhere. Being free to do these things means (among other things) that do not have to ask or pay for permission.

You should also have the freedom to make modifications and use them privately in your work or play, without even mentioning that they exist. If you publish your changes, you do not have to notify anyone in particular or any particular way.

The freedom to use a program means the freedom for any person or organization to use in any type of computer system for any kind of work, and without obligation to notify the developer or any other specific entity.

The freedom to redistribute copies must include both binary or executable forms of the program and its source code, whether modified or unmodified versions (Distributing programs in runnable form is necessary to free operating systems are easy to install). It's okay if there is no way to produce an executable binary or a specific program (since some languages do not have this capability), but you have the freedom to redistribute such forms should you find or develop a way to create them.

For the freedoms to make changes and to publish improved versions make sense, you have access to source code. Therefore, the ability to access the source code is a necessary condition for free software.

In order for these freedoms to be real, must be irrevocable as long as you do nothing wrong, if the software developer has the power to revoke the license, you have given no reasons, the software is not free.

Are acceptable, however, certain kinds of rules about how to distribute free software, while not in conflict with the central freedoms. For example, copyleft is the rule that when the program is redistributed, you can not add restrictions to deny other people the central freedoms. This rule does not conflict with the central freedoms, but rather protects them.

'Free software' does not mean 'non-commercial. " A free program must be available for commercial use, development and commercial distribution. Commercial development of free software is no longer unusual; free commercial software is very important.

But the free software 'copyleft' also exists. We believe that there are important reasons why it is better to use 'copyleft', but if your program is free software without being 'copyleft', we can use them anyway.

When we speak of free software, it is best to avoid terms such as `gift 'or` free', because those terms imply that the issue is price, not freedom.