Open source software refers to computer software and the
availability of its source code as open source under an
open source license to study, change, and improve its
design.
The GNU General Public License (GNU GPL or simply GPL) is a
free software license. The GPL grants the recipients of a
computer program the following rights, or "freedoms":
the freedom to run the program, for any purpose.
the freedom to study how the program works, and modify it
the freedom to redistribute copies
the freedom to improve the program, and release the
improvements to the public
Open Source Software in Wikipedia