I have installed some hardware drivers from the contrib non-free repositories in order to get my device working properly, e.g. Realtek WLAN adapter, NVIDIA graphics driver etc. Also I have installed Skype and TeamViewer directly from their official websites and vrms tells me that those are non-free. So I wonder does using this non-free software constitute piracy?
Does installing non-free software from Debian non-free repositories constitute piracy?
debian;free software
No, it is not piracy.  The common parlance is that there is free as in speech, which is to say it is unfettered by restrictions on distribution and comes with a copy of (or links to) the original source code so that you can make your own changes to the software; and that there is free as in beer, which is to say that you can obtain it free of charge, but you don't get the recipe (i. e. the source code) or the rights to create derivative works from it.vrms defines free here thusly:Free software means software that respects users' freedom and  community. Roughly, it means that the users have the freedom to run,  copy, distribute, study, change and improve the software. Thus, free  software is a matter of liberty, not price. To understand the  concept, you should think of free as in free speech, not as in  free beer. We sometimes call it libre software, borrowing the  French or Spanish word for free as in freedom, to show we do not  mean the software is gratis.It goes on to give the following specificity for what qualifies as free:A program is free software if the program's users have the four  essential freedoms:The freedom to run the program as you wish, for any purpose.The freedom to study how the program works, and change it so it does your computing as you wish. Access to the source code is a precondition for this. The freedom to redistribute copies so you can help your 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. Access to the source code is a precondition  for this.