Imagine that you go to a restaurant and you enjoy a fantastic meal. The next day you might want to prepare the same meal at home for your friends.
Unfortunately, that is impossible because you don't have the recipe. You can always return to the same restaurant to enjoy the same meal, but even if you know the taste and texture of the food, you don't know how to reproduce it exactly.
In computers, it is the same as with software. Most software is distributed without the recipe (called source code). It is forbidden to attempt to understand the workings of the program. This is what we call proprietary software. You may not share it with your friends, and you may not make any modifications to adapt the software to your specific needs.
On the other hand, a free software application grants you many freedoms :
- the freedom to run the program, for any purpose (freedom 0)
- the freedom to study how the program works, and adapt it to your needs (freedom 1). Access to the source code is a precondition for this
- the freedom to redistribute copies so you can help your neighbor (freedom 2)
- the freedom to improve the program, and release your improvements to the public, so that the whole community benefits. (freedom 3). Access to the source code is a precondition for this
With a free software program you have the meal, the recipe, the right to redistribute (or sell) the meal and the right to modify the recipe and the right to redistribute your modified version of the meal.