This page contains links to official definition of Free Software by the FSF. This page also contains a short description of nonfree software (also called proprietary software).

Free Software

The official definition is at https://www.gnu.org/philosophy/free-sw.html.

Quoted from FSF's definition:

A program is free software if the program's users have the four essential freedoms:

• The freedom to run the program as you wish, for any purpose (freedom 0).
• The freedom to study how the program works, and change it so it does your computing as you wish (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 distribute copies of your modified versions to others (freedom 3). By doing this you can give the whole community a chance to benefit from your changes. Access to the source code is a precondition for this.

End of quotation.

Free software is called free because the user is free. Free software is related to freedom, not price.

Nonfree Software

A program is nonfree software if the program fails to give the four essential freedoms to the users.

Nonfree software is called nonfree because the user is nonfree. Nonfree software does not mean paid, nonfree means the users have no freedom. Nonfree software is also called proprietary software.