Whalerman, the nfa in an extremely interesting subject and you should google it and learn more about it. I was pleasantly shocked when I found out about things I could legally buy just by paying a $200 tax stamp and getting a background check.
As for people using terms (nfa terms) that you are not familiar with, you are currently on an NFA thread.
Interesing nfa topics.
destructive devices (DD)
Silencers (mufflers, suppressors, moderators) of which I own two
machine guns
short barrel rifles (sbr)
short barrel shotguns (sbs)
..........one of the interesting subjects here is why is my Taurus judge (.410 shotshell pistol) legal. Answer, the barrel is rifled.
any other weapons (aow) penguns cane guns etc.
Another interesting angle, is that they don't care how long of a barrel I put on my Contender pistol. If the barrel is 22", its still a pistol. However, 12" or longer, then Tennessee no longer recognizes it as a hand gun for carry purposes.
Some states do not allow some or all NFA firearms. Fortunatly for me, TN allows all NFA firearms. That's more NFA terminoligy, a silencer is called an NFA firearm.