The term "open source software" refers to any software of which the code is open to use, modification, and redistribution under a variety of licensing structures designed to keep the code accessible and in the public domain.

In the legal domain, two of the most active groups in the open source software movement are the Open Source Initiative (OSI) and the Free Software Foundation (FSF).

The OSI is a nonprofit organization that approves software licenses that are consistent with its definition of open source standards. If one considers the OSI as working mainly in tandem with software producers, one can think of the FSF as working equally in tandem with software users. This is reflected in the FSF's definition of free software.

More Free Software Matters: Free Software or Open Source? Eben Moglen, 2000