1. "Open-source" describes a set of political values espoused by many on the Internet. When creating software, a programmer will write code. Code is the "source" from which the software is built. This source code is then compiled into object binaries. It is not feasable to reconstruct the source code from the binaries, which means that somebody using software cannot see the source code from which it was built. The political view is that people should be able to view the source, that is should be "open" for reading by anybody. The primary reason is that open-source increases "freedom". People are free to make changes as they like to the source-code, thereby fixing bugs or adding features to their software. There is also a level of paranoia involved: people fear that closed-source they can't read may be doing something subversive, such as secretly monitoring people for the government. Controversey: Open-source advocates believe that it is beneficial for the following reasons: security Security is founded upon the principle of peer review. This is especially true in the world of crypto, where nothing is accepted without years of vetting by members of the crypto community. In the same fashion, many paranoids will trust only peer-reviewed, open-source software. However, as of 2001, both open-source and closed-source have been the source of massive security problems (such as the many popular Linux worms). cost Open-source software licenses are usually free. However, since software licenses for many products are much smaller than operational costs, it price is not as important as other things. For example, BIND and Sendmail are popular not so much for their free licenses, but more for the fact that they have been the standard for more than 15 years. These products are well understood, and therefore cheap for companies to operate. stability and bugs The peer-review model suggests that bugs can be easily found and fixed. However, both open-source and closed-source suffer from the fact that source-code is a constantly moving target. In both cases, new code is being written faster than existing code is being fixed. There are some open-source projects (e.g. OpenBSD) where developers concentrate on stabilizing code rather than moving forward to the latest and greatest features. However, some people think that projects like Linux are too fast a moving target to ever quite stabilize. Since the source-code is open, developers can easily change it to add features. However, few people are developers, and the code is often so poorly documented, adding changes to it can often be more of a burden than starting over from scratch. Example: The following are well known open-source projects: Linux, Apache, sendmail, BIND, Samba, Perl, Mozilla, MySQL From Hacking-Lexicon