ATSC is the digital standard used by North American digital television broadcasters in the United States and Canada, South Korea also uses the ATSC standard. 

DVB-T is a European standard and will not work in North America. If your in North America make sure you get a ATSC card and not DVB-T card as you may find on some auction sites.

QAM is the format most North American Digital cable systems use for their digital channels. Also note that you will only be able to receive Un-Encrypted QAM channels with the cards listed above.

NTSC is the format that North American Analog channels are broadcast in, Same goes with Cable TV analog channels.