Free software is a matter of the users' freedom to run, copy, distribute, study, change and improve the software. More precisely, it refers to four kinds of freedom for the users of the software:

• The freedom to run the program, for any purpose.
• The freedom to study how the program works, and adapt it to the user's needs.
• The freedom to redistribute copies so that the users can help each other.
• The freedom to improve the program, and release the improvements to the public.

In order for the freedoms to make changes, and to publish improved versions, to be meaningful, the user must have access to the source code of the program. Therefore, accessibility of source code is a necessary condition for free software. The user may or may not have paid money to get copies of free software. But regardless of how one got copies, he or she always have the freedom to copy and change the software, even to sell copies.

Free software does not mean non-commercial. The word "Free" here elucidate the above four freedoms and not "free of cost". A free program may be available for commercial use, commercial development, and commercial distribution. Commercial development of free software is no longer unusual; such free commercial software is very important.

The GNU Project : The GNU Project was conceived in 1983 as a way of bringing back the cooperative spirit that prevailed in the computing community in earlier days and removing restrictions imposed by the owners of proprietary software. The first item on the free software agenda was a free operating system. In the 1990s, the GNU operating system was developed, with Linux functioning as its kernel, thus providing a complete free system - the GNU/Linux system. The GNU Project is not limited to operating systems. It aims to provide a whole spectrum of software including compilers, editors and application software such as a spreadsheet.

Free and Open Source Software : In the GNU project, the aim is to give all users the freedom to redistribute and change GNU software. Licenses to the proprietary software are (usually) fairly restrictive in regards to what one is (and is not) allowed to do with the software in question. One may typically be only allowed to use one license per computer, he or she may not be allowed to pass copies on to any friends, most certainly not permitted to resell it, and in no way allowed to make changes to the software. Thus, the business world restricts the use of these software packages with copyright agreements. In contrast to the copyright agreements for proprietary software, GNU software are copylefted. Copyleft says that anyone who redistributes the software, with or without changes, must pass along the freedom to further copy and change it. Copyleft guarantees that every user has freedom. Thus Copyleft is a general method for making a software package free and requiring all modified and extended versions of the program to be free software as well. A very close, but different concept is the Open Source Software. Those who use the term Open Source Software tend to emphasize only on technical advantages of the software (such as better reliability and security) whose source codes are available. Thus one who modifies open source software is not bound to redistribute the version with copyleft agreement and some restrictions in license agreements are acceptable by the Open Source Community. However, as the two concepts are very close, we consider both Free and Open Source Software within the same category and stick to the term free / open source software (FOSS or F/OSS).A few people make the mistake by saying that FOSS is non-commercial or public domain. FOSS programs are also not always in the public domain. The term public domain software has a specific legal meaning -- software that has no copyright owner.

FOSS has many strong cost advantages, such as:

• FOSS costs less to initially acquire.
• Upgrade/maintenance costs are typically far less.
• FOSS does not impose license management costs.
• FOSS can often use older hardware more efficiently than proprietary systems, yielding smaller hardware costs and sometimes eliminating the need for new hardware.