Hey Miltos,
Thank you for the compliment I am pleased you like the site and are finding it usefel. As we are all here to learn I always tell people that the only idiotic question is the question that someone has and does not ask so we always welcome any and all questions. Also from this post your english also seems perfect to me, and even if it wasn't we encourage and welcome people from all over the world here so we are glad to hear from you.
Trading is similar to a sports game in the sense that when you are trading you are playing against all of the other traders out there. So your edge in trading is what about your trading makes you better than other traders out there who are trying to make money at your expense?
This could be hundreds of things including a technical strategy that allows you to get into trends when they are forming and get out with profits more than you loose, it could be better technology than everyone else, it could be greater patience than other traders or reallyanything that makes you better or gives you the "edge" that you need to beat all the other traders out there who are all playing the same game you are.
Here is an article from one of my favorite bloggers which goes into this in a little more detail:
The Big Picture | Find Your Trading Edge
Hope that helps and hope to hear more from you in the future. If there are any other questions or comments on this one please feel free to hit the reply button.
Best Regards,
Dave