GNU

A project of the Free Software Foundation to write a free version of the Unix operating system. The acronym was coined by Richard Stallman of MIT.

GNU is an operating system that began development in 1984. By 1991, only the kernel was lacking. Linux filled that last gap, and the combination, the GNU-Linux operating system, is what people use today.

The GNU General Public License (known as "GNU GPL" or simply "GPL") is a widely used free software license used by the GNU/Linux operating system, originally written by Richard Stallman for the GNU project. The GPL is the most popular and well known example of the "strong copyleft license" that requires derived works to be available under the same copyleft. Under this philosophy, the GPL is said to grant the recipients of a computer program the rights of the free software definition and uses copyleft to ensure the freedoms are preserved, even when the work is changed or added to. (This is in distinction to permissive free software licences, of which the BSD licenses are the standard examples.