Free Software or Libre (Libre is the most common Spanish adjective for “free”) software are the softwares that allows user to do to any kind of work he/she wants as well as he can modify, add new features and he has freedom to distribute the changed version also. A software is said to be free if it gives user ultimate freedom to do things the way he wants.
The term “free software” is sometimes misunderstood—it has nothing to do with price. It is about freedom. Here, therefore, is the definition of free software: a program is free software, for you, a particular user, if:
You have the freedom to execute the program, the way you want and to serve any kind of purpose.
You have the freedom to study how the program works and you are free to modify the program to suit your needs
You have the freedom to redistribute copies, either gratis or for a fee. So that you can help others and also you can earn profit too.
You have the freedom to distribute modified versions of the program, so that the community can benefit from your improvements.
The Free Software Directory maintains a large database of free-software packages. Some of the best-known examples include the Linux kernel, the BSD and Linux operating systems, the GNU Compiler Collection and C library; the MySQL relational database; the Apache web server; and the Sendmail mail transport agent.