When a software program is open source, it means the program's source code is freely available to the public. Unlike commercial software, open source programs can be modified and distributed by anyone and are often developed as a community rather than by a single organization. For this reason, the phrase "open source community" is commonly used to describe the developer of open source software development projects.
Since open source software is free to use, there is typically no technical support included with the software. Instead, users may need to rely on Web forums and user discussions to report bugs or get answers to their questions. Fortunately, the most popular open source programs have an abundance of helpful resources available on the Web. Some of the most well-known open source projects include the Linux operating system, the Mozilla Firefox Web browser, and the OpenOffice.org productivity suite. Each of these projects have been developed by a community of developers and have gained levels of popularity that rival their commercial counterparts.
Open source software can be a cost-effective way to run many types of programs on your computer. Just remember that since the programs are not backed by a commercial company, if you have problems using the software, you will most likely not be able to obtain technical support from the developer. Of course, if you like to figure things out on your own or participate in online discussions, open source software may be just right for you.
Source from : http://www.techterms.com/definition/opensource