Open Source Software (OSS), sometimes referred to as Free and Open Source Software (FOSS), is computer software that includes source code that can be used and modified by the user without paying licensing fees or royalties. OSS is not public domain software or freeware. It is copyrighted and includes a license agreement restricting its use, modification, and distribution. Potential benefits of OSS include better quality, higher reliability, more flexibility, lower cost, and not being locked into a single vendor. DoD policy treats OSS in a manner similar to Commercial off-the-Shelf (COTS) software. 
The Open Source Initiative (OSI) contains more information on open source and open source licenses. The OSI is a non-profit corporation which maintains the complete Open Source Definition consisting of ten requirements which software must meet to be considered open source, and the OSI license review process which, through a public review process, ensures that licenses and software labeled as “open source” comply with the Open Source Definition and conform to existing community norms and expectations. [1,2]
DoD and the Air Force have established as a priority developing policy and guidance to leverage the benefits of Open Technology Development (OTD) and OSS. The DoD Open Technology Development Roadmap states; “DoD needs to use open technology design and development methodologies to increase the speed at which military systems are delivered to the warfighter, and accelerate the development of new, adaptive capabilities that leverage DoD‘s massive investments in software infrastructure.” 
- OSS license requirements may include making the source code available, publishing a copyright notice, placing a disclaimer of warranty on distributed copies, and giving any recipient of the program a copy of the license.
AcqLinks and References:
-  USAF Weapons System Software Management Guide – Section 3
-  Defense Acquisition Guidebook (DAG) – Chapter 4
-  Open Technology Development Roadmap, Ver 3.1 – April 2006