In simple words, open source is a program for which the source code is available publicly for use and/or modification from its original design and structure. Open source code is collaborative efforts in which programmers improve upon the existing codes and the new improvements are shared within the community of developers. Open source came to existence when big corporations started charging huge amount against proprietary software.
The open source model is about concept of parallel yet different agendas and differing approach in producing anything. It is a contrasting approach of centralized models of development that being used by commercial software companies.
Open-source software development is peer based production that relies on exchange of knowledge and collaboration of efforts. And this happens in all the respects of development of the end-product, source-material, “blueprints”, and documentation process. Everything remains available almost at no cost.