What is open source software and how do I benefit from it?

u get to see and use the code …. and whenever u want to add anything u should also give them the right to see, use the code…

Open source describes practices in production and development that promote access to the end product’s source materials—typically, their source code. Some consider it as a philosophy, and others consider it as a pragmatic methodology. Before open source became widely adopted, developers and producers used a variety of phrases to describe the concept; the term open source gained popularity with the rise of the Internet and its enabling of diverse production models, communication paths, and interactive communities.[1] Subsequently, open source software became the most prominent face of open source practices.

The open source model can allow for the concurrent use of different agendas and approaches in production, in contrast with more centralized models of development such as those typically used in commercial software companies.[2] “Open source” as applied to culture defines a culture in which fixations are made generally available. Participants in such a culture are able to modify those products and redistribute them back into the community.

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http://en.wikipedia.org/wiki/Open_source