Free software is software that can be used, studied, and modified without restriction. In order to make this possible, the source code must be available to the end user, who is usually notified of this via a free software licence. Software can also be made free software by putting the source code in the public domain.
The first formal definition of free software was published by the Free Software Foundation in February 1986. That definition, written by Richard Stallman, is still maintained today and states that software is free software if people who receive a copy of the software have the following four freedoms:
- Freedom 0: The freedom to run the program for any purpose.
- Freedom 1: The freedom to study and modify the program.
- Freedom 2: The freedom to copy the program so you can help your neighbor.
- Freedom 3: The freedom to improve the program, and release your improvements to the public, so that the whole community benefits.
Freedoms 1 and 3 require source code to be available because studying and modifying software without its source code is highly impractical.
Thus, free software means that computer users have the freedom to cooperate with whom they choose, and to control the software they use.