COPYLEFT what is that?

Today I am going to focus on the term Copyleft andwhy is it important to consider this in your works or proects as an author. Let's check it out:

First of all , what is Copyleft?

Copyleft is a creation license that consists on releasing a computer program, a work of art or any other type of document for its copying, modification and redistribution. Which means leave it for public use without restrictions (this is the strong definition). It is a legal practice that is carried out in the exercise of copyright. 

Since copyleft is the opposite of copyright, the terms 'left' and 'right' are used to demonstrate the  opposite meaning. Even the representation of it is diferent: Copyright appears represented as a C in a normal way and copyleft reversed.

But are there types of coypleft or categories maybe? The answer is yes of course, there are two main categories: Strong and weak. 

    -If we focus on strong copyleft we find out that is when for example an author of a software makes the code open source so anyone can use it or at least without many problems over restrictions. An easy example is General Public License (GNU) which you can use this software on your computer for free.

    -The other part of copyleft as we said is weak copyleft and of course it is also permissive on the users but it results on a free part of a licensed software or project. So this means that you can use the whole program without changing the source of the part which

has weak copyleft. Basically you can use it but not change it. For example the Mozilla Public License (MPL)

So now I wanted to ask you something, if you create a new software and it gets "trendy" would you make copyright about it? Or you would leave for free use?