It’s clear that in English the word “Free” can mean both Free of charge (meaning no price tag) and Free as in Free to do whatever you want. This linguistic conflict doesn’t exist in other languages.
Richard Stallman, founder of Free Software Foundation and Author of GNU General Public License puts it in a very simple way:
“Free as in freedom not free as in free beer“
He states that there are Four essential freedoms that any software needs to have to be considered “Free Software”. We can summarize these four freedoms as follows:
The freedom to run the program as you wish, for any purpose
The freedom to change it so it does your computing as you wish. Hence, Free Access to the source code is a precondition for this.
The freedom to share the software, i.e. redistribute copies so you can help thy neighbor.
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. Which implies also that access to the source code is a precondition for this.
Open-Source is not “Free”
Despite the fact that you might be using the words “Open-Source” and “Free Softwrae” interchangeably. However, Stallman insists that having access to the source code is only one of the Four Freedoms.
For example, Famous Game engines such as UE4 might be open-source, Nevertheless, they are not according to Stallman, “Free”. While Godot, another uprising Game engine is a 100% Free Software. As it is free to use, modify or share.
Other Famous Free software packages include: Blender, GIMP, KRITA…. and the list goes on and on.
The accessebility to the source code opened the door for a whole new community collaborating to these softwares even though some of these softwares now have stable and huge funding.