Open-source
Term used to describe a program or file that can be freely modified by anyone, allowing users to make the program perform the way he, she or their company or organization needs it to operate or perform.
There are numerous open source licensing or agreements that the open source program or file may follow. Therefore, it is best to refer to the program's licensing agreement to see what the original developer allows and prohibits. The licensing agreement is commonly included in the header or footer of the actual file or included with the program or file itself.
Also see: FOSS, GPL, OIN, OSI, OSS, SourceForge