All your questions will be answered here http://forums.afterdawn.com/thread_view.cfm/232314. Honestly, you could find it in a dictionary!
I'm not being a jerk, I'm just tired of people that make threads that are easily answered without searching. I apologize, but maybe next time you will search before you post. Go here, http://www.webopedia.com/TERM/N/NTSC.html, it answers your question.