The GNU-GPL license is an open source software license.

One of the most well known symbols of the free software movement, which is sometimes called FOSS, for “Free open source software”. GNU is an open source operating system, upwardly compatible with Unix.

Richard Stallman started working on GNU at MIT in 1984, and founded the Free Software Foundation in 1985 to help his efforts. When GNU was incorporated with the Linux kernel, the combination became the GNU/Linux system, now found in various different software distributions.

GPL stands for “General Public License”. GPL licenses must contain what are referred to as the ”four freedoms”, which are:

• The freedom to run the program, for any purpose (freedom 0).

• The freedom to study how the program works, and change it to make it do what 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 improve the program, and release your improvements (and modified versions in general) to the public, 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 of these freedoms.

Other resources:

• GNU’s webpage on GPL licenses
• Creative Commons webpage on GPL
• Opensource’s page on GPL
• Linux.org’s page on GNU
• Wikipedia article on GNU/GPL