The concept is meant to be Free as in speech, not free as in beer - although most projects account for both. This means that you have the right to modify and redistribute packages with certain license obligations(such as keeping the open source license when redistributing).
Most times when you get software, you only get binary files - which do not reveal much of their engineering or design. In Open source projects, the whole of the design is open, so you can learn a lot from them.
The idea is that everyone benefits - and your modifications benefit the community who originally created the software. People may stand on the shoulders of giants when engineers need not reinvent the wheel.
Surprisingly, the idea is also relatively profitable, generally to be gained in customising solutions, something which is a great deal easier in this realm, as well as by offering support and even just accepting liability, a function relatively valuable in the business world.
The concept has extended past software, and into hardware, music, creative writing, video and in fact just about anything one can imagine. It is seen by some as the arch-nemesis of intellectual property.
This is only a small, but representative selection of the licenses. Many projects also have their own licenses which are variants of the above or have some common terms, examples are the Mozilla License and the PSL - Python Software License.
As stated above, much of the software used to run this site is open source. We also contribute back and release small code projects under the GPL. Contributions include bug fixing, bug reporting and community support.
This article was not written by a lawyer. OrionRobots is not able to provide legal advice, and this page is designed as encyclopaedic information only. Please contact a lawyer if you seek legal advice on Open Source.