Free In Open Source Software

Free software is a matter of the user’s freedom to run, copy, distribute, study, change and improve the software. More precisely, it means that the program's users have the four essential freedoms:

• The freedom to run the program, for any purpose.
• The freedom to study how the program works, and change it to make it do what you wish. Access to the source code is a precondition for this.
• The freedom to redistribute copies.
• The freedom to distribute copies of your modified versions to others. By doing this you can give the whole community a chance to benefit from your changes. Access to the source code is a precondition for this.

A program is free software if users have all of these freedoms.Thus, we should be free to redistribute copies, either with or without modifications, either gratis or charging a fee for distribution.

We also should have the freedom to make modifications and use them privately in our own work without even mentioning that they exist. If we do publish our changes, we should not be required to notify anyone in particular, or in any particular way.

The freedom to run the program means the freedom for any kind of person or organization to use it on any kind of computer system, for any kind of overall job and purpose, without being required to communicate about it with the developer or any other specific entity.In this freedom, it is the user's purpose that matters, not the developer's purpose you as a user are free to run the program for your purposes, and if you distribute it to someone else, she is then free to run it for her purposes, but you are not entitled to impose your purposes on her.

The freedom to redistribute copies must include binary or executable forms of the program, as well as source code, for both modified and unmodified versions. (Distributing programs in runnable form is necessary for conveniently installable free operating systems.) It is OK if there is no way to produce a binary or executable form for a certain program (since some languages don't support that feature), but you must have the freedom to redistribute such forms should you find or develop a way to make them. 

Reference:http://en.wikipedia.org/wiki/Free_and_open_source_software