A technology, product or software which is not owned exclusively by a single company, which has information on the technology, the product or the software's source code freely available and which is distributed under a license that guarantees the right to access, redistribute, modify, and use the information on the technology, the product or the software's source code freely.
A software program whose source code is made available for use or modification as users or other developers see fit. (Generally, the makers of proprietary software have not made source code available.) Open source software is usually developed as a public collaboration and made freely available. Sometimes these third-party modifications are incorporated into later versions of the software.