Tim O’Reilly’s definition of open source

From Tim O’Reilly’s “Lessons from open source software development”, Communications of the ACM 41 (4): 33-7:

Open source is a term that has recently gained currency as a way to describe the tradition of open standards, shared source code, and collaborative development behind software such as the Linux and FreeBSD operating systems, the Apache Web server, the Perl, Tcl, and Python languages, and much of the Internet infrastructure, including Bind (The Berkley Internet Name Daemon servers that run the Domain Name System), the Sendmail mail server, and many other programs. … [But] open source … means more than the source code is available. The source must be available for redistribution without restriction and without charge, and the license must permit the creation of modifications and derivative works, and must allow those derivatives to be redistributed under the same terms as the original work.