Open Source Software:

Open Source Software (OSS) is software that comes with source code, and importantly also provides rights (typically reserved for copyright holders) to study, change and improve the software. This development happens in a larger collaborative environment, without any direct objective of the software's commercial success.   

Primary objectives of the Open Source movement are as following:  

• Encourage innovation at the grass-root level and facilitate collaborative software development involving individual talent than it being the prerogative of the large companies.  
• Reduce the software cost.  
• Improve quality and security  
• Avoid forced lock-in to vendor's proprietary software.   

Open Source Initiative (OSI) is the patron of the Open Source Definiton (OSD) and is the community-recognized body to evaluate and approve the software as OSD compliant. Some key criterion for OSD compliance are mentioned below:

•   Free Redistribution : The license should allow any party to sell or give away the software as a component of a larger software distribution containing programs from multiple sources. The license shall not require a royalty or other fee for such sale.   
• Source Code:  The program must include source code, and must allow distribution in source code as well as in executable form. Where some form of a product is not distributed with source code, there must be a well-publicized means of obtaining the source code for no more than a reasonable reproduction cost preferably, downloading via the Internet without charge.