Free Open Source Software
What's all the FOSS?
Free/open source software (F/OSS) is software for which the human-readable source code is made available to the user of the software to use as they see fit. This means that someone capable of programming can then modify the code in order to fit the software to their needs.
Software is then modified and can be redistributed, thereby improving and adapting the software. In this manner people share and collaborate to develop software, often saving needless duplication of effort. In this manner the software evolves at a rate unmatched by traditional proprietary software.
Open Source software is becoming increasing important in computing, and is seen as a major threat to the dominance of Microsoft in home and business computing, both on the desktop where microsoft is currently strong and in the server market where other Unix flavours are the norm.
In some respects this model of sharing is similar to the early days of computing, before commercial software was available. The original programming was done by researchers in laboratories who often shared their developments. However today there are a number of different motivations for sharing code, and different views of what 'free' or 'open' should mean, code is usually distributed with a license which descibes the conditions it is shared under.
The license which gives the most freedom over the code is the open-bsd style license, this allows the code to be used in any way.
Another common license is the GPL, this allows the code to be modified in any way, with the provision that you cannot distribute any programs you write without also distributing the human readable source code.
The BSD-style licenses are specifically designed to allow conversion of an OSS/FS program into a proprietary program. The GPL license was specifically designed to prevent this.
Read more at opensource.org