1) In general, open source refers to any program whose source code is made available for use or modification as users or other developers see fit. Open source software is usually developed as a public collaboration and made freely available.
2) Open Source is a certification mark owned by the Open Source Initiative (OSI). Developers of software that is intended to be freely shared and possibly improved and redistributed by others can use the Open Source trademark if their distribution terms conform to the OSI's Open Source Definition. To summarize, the Definition model of distribution terms require that:
- The software being distributed must be redistributed to anyone else without any restriction.
- The source code must be made available (so that the receiving party will be able to improve or modify it).
- The license can require improved versions of the software to carry a different name or version from the original software.
The idea is very similar to that behind free software and the Free Software Foundation.